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2013-06-27sched: Update cpu load after task_tickAlex Shi
To get the latest runnable info, we need do this cpuload update after task_tick. Signed-off-by: Alex Shi <alex.shi@intel.com> Reviewed-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1371694737-29336-6-git-send-email-alex.shi@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-27sched: Fix sleep time double accounting in enqueue entityAlex Shi
The woken migrated task will __synchronize_entity_decay(se); in migrate_task_rq_fair, then it needs to set `se->avg.last_runnable_update -= (-se->avg.decay_count) << 20' before update_entity_load_avg, in order to avoid sleep time is updated twice for se.avg.load_avg_contrib in both __syncchronize and update_entity_load_avg. However if the sleeping task is woken up from the same cpu, it miss the last_runnable_update before update_entity_load_avg(se, 0, 1), then the sleep time was used twice in both functions. So we need to remove the double sleep time accounting. Paul also contributed some code comments in this commit. Signed-off-by: Alex Shi <alex.shi@intel.com> Reviewed-by: Paul Turner <pjt@google.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1371694737-29336-5-git-send-email-alex.shi@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-27sched: Set an initial value of runnable avg for new forked taskAlex Shi
We need to initialize the se.avg.{decay_count, load_avg_contrib} for a new forked task. Otherwise random values of above variables cause a mess when a new task is enqueued: enqueue_task_fair enqueue_entity enqueue_entity_load_avg and make fork balancing imbalance due to incorrect load_avg_contrib. Further more, Morten Rasmussen notice some tasks were not launched at once after created. So Paul and Peter suggest giving a start value for new task runnable avg time same as sched_slice(). PeterZ said: > So the 'problem' is that our running avg is a 'floating' average; ie. it > decays with time. Now we have to guess about the future of our newly > spawned task -- something that is nigh impossible seeing these CPU > vendors keep refusing to implement the crystal ball instruction. > > So there's two asymptotic cases we want to deal well with; 1) the case > where the newly spawned program will be 'nearly' idle for its lifetime; > and 2) the case where its cpu-bound. > > Since we have to guess, we'll go for worst case and assume its > cpu-bound; now we don't want to make the avg so heavy adjusting to the > near-idle case takes forever. We want to be able to quickly adjust and > lower our running avg. > > Now we also don't want to make our avg too light, such that it gets > decremented just for the new task not having had a chance to run yet -- > even if when it would run, it would be more cpu-bound than not. > > So what we do is we make the initial avg of the same duration as that we > guess it takes to run each task on the system at least once -- aka > sched_slice(). > > Of course we can defeat this with wakeup/fork bombs, but in the 'normal' > case it should be good enough. Paul also contributed most of the code comments in this commit. Signed-off-by: Alex Shi <alex.shi@intel.com> Reviewed-by: Gu Zheng <guz.fnst@cn.fujitsu.com> Reviewed-by: Paul Turner <pjt@google.com> [peterz; added explanation of sched_slice() usage] Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1371694737-29336-4-git-send-email-alex.shi@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-27sched: Move a few runnable tg variables into CONFIG_SMPAlex Shi
The following 2 variables are only used under CONFIG_SMP, so its better to move their definiation into CONFIG_SMP too. atomic64_t load_avg; atomic_t runnable_avg; Signed-off-by: Alex Shi <alex.shi@intel.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1371694737-29336-3-git-send-email-alex.shi@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-27Revert "sched: Introduce temporary FAIR_GROUP_SCHED dependency for ↵Alex Shi
load-tracking" Remove CONFIG_FAIR_GROUP_SCHED that covers the runnable info, then we can use runnable load variables. Also remove 2 CONFIG_FAIR_GROUP_SCHED setting which is not in reverted patch(introduced in 9ee474f), but also need to revert. Signed-off-by: Alex Shi <alex.shi@intel.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/51CA76A3.3050207@intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-20Merge branch 'sched-urgent-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler fixes from Ingo Molnar: "Two smaller fixes - plus a context tracking tracing fix that is a bit bigger" * 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: tracing/context-tracking: Add preempt_schedule_context() for tracing sched: Fix clear NOHZ_BALANCE_KICK sched/x86: Construct all sibling maps if smt
2013-06-19sched: Don't mix use of typedef ctl_table and struct ctl_tableJoe Perches
Just use struct ctl_table. Signed-off-by: Joe Perches <joe@perches.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1371063336.2069.22.camel@joe-AO722 Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Remove WARN_ON(!sd) from init_sched_groups_power()Viresh Kumar
sd can't be NULL in init_sched_groups_power() and so checking it for NULL isn't useful. In case it is required, then also we need to rearrange the code a bit as we already accessed invalid pointer sd to get sg: sg = sd->groups. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/2bbe633cd74b431c05253a8ce61fdfd5066a531b.1370948150.git.viresh.kumar@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Fix memory leakage in build_sched_groups()Viresh Kumar
In build_sched_groups() we don't need to call get_group() for cpus which are already covered in previous iterations. Calling get_group() would mark the group used and eventually leak it since we wouldn't connect it and not find it again to free it. This will happen only in cases where sg->cpumask contained more than one cpu (For any topology level). This patch would free sg's memory for all cpus leaving the group leader as the group isn't marked used now. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/7a61e955abdcbb1dfa9fe493f11a5ec53a11ddd3.1370948150.git.viresh.kumar@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Use cached value of span instead of calling sched_domain_span()Viresh Kumar
In the beginning of build_sched_groups() we called sched_domain_span() and cached its return value in span. Few statements later we are calling it again to get the same pointer. Lets use the cached value instead as it hasn't changed in between. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/834ecd507071ad88aff039352dbc7e063dd996a7.1370948150.git.viresh.kumar@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Create for_each_sd_topology()Viresh Kumar
For loop for traversing sched_domain_topology was used at multiple placed in core.c. This patch removes code redundancy by creating for_each_sd_topology(). Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/e0e04542f54e9464bd9da54f5ccfe62ec6c4c0bc.1370861520.git.viresh.kumar@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Don't set sd->child to NULL when it is already NULLViresh Kumar
Memory for sd is allocated with kzalloc_node() which will initialize its fields with zero. In build_sched_domain() we are setting sd->child to child even if child is NULL, which isn't required. Lets do it only if child isn't NULL. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/f4753a1730051341003ad2ad29a3229c7356678e.1370861520.git.viresh.kumar@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Don't initialize alloc_state in build_sched_domains()Viresh Kumar
alloc_state will be overwritten by __visit_domain_allocation_hell() and so we don't actually need to initialize alloc_state. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/df57734a075cc5ad130e1ae498702e24f2529ab8.1370861520.git.viresh.kumar@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Optimize build_sched_domains() for saving first SD node for a cpuViresh Kumar
We are saving first scheduling domain for a cpu in build_sched_domains() by iterating over the nested sd->child list. We don't actually need to do it this way. tl will be equal to sched_domain_topology for the first iteration and so we can set *per_cpu_ptr(d.sd, i) based on that. So, save pointer to first SD while running the iteration loop over tl's. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/fc473527cbc4dfa0b8eeef2a59db74684eb59a83.1370436120.git.viresh.kumar@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Remove unused params of build_sched_domain()Viresh Kumar
build_sched_domain() never uses parameter struct s_data *d and so passing it is useless. Remove it. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/545e0b4536166a15b4475abcafe5ed0db4ad4a2c.1370436120.git.viresh.kumar@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Femove the useless declaration in kernel/sched/fair.cMichael Wang
default_cfs_period(), do_sched_cfs_period_timer(), do_sched_cfs_slack_timer() already defined previously, no need to declare again. Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/51AD8808.7020608@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Refine the code in unthrottle_cfs_rq()Michael Wang
Directly use rq to save some code. Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/51AD87EB.1070605@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched/rt: Simplify pull_rt_task() logic and remove .leaf_rt_rq_listKirill Tkhai
[ Peter, this is based off of some of my work, I ran it though a few tests and it passed. I also reviewed it, and added my SOB as I am somewhat a co-author to it. ] Based on the patch by Steven Rostedt from previous year: https://lkml.org/lkml/2012/4/18/517 1)Simplify pull_rt_task() logic: search in pushable tasks of dest runqueue. The only pullable tasks are the tasks which are pushable in their local rq, and no others. 2)Remove .leaf_rt_rq_list member of struct rt_rq and functions connected with it: nobody uses it since now. Signed-off-by: Kirill Tkhai <tkhai@yandex.ru> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/287571370557898@web7d.yandex.ru Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19Merge branch 'sched/urgent' into sched/coreIngo Molnar
Merge in fixes before applying ongoing new work. Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-06-19sched: Fix clear NOHZ_BALANCE_KICKVincent Guittot
I have faced a sequence where the Idle Load Balance was sometime not triggered for a while on my platform, in the following scenario: CPU 0 and CPU 1 are running tasks and CPU 2 is idle CPU 1 kicks the Idle Load Balance CPU 1 selects CPU 2 as the new Idle Load Balancer CPU 2 sets NOHZ_BALANCE_KICK for CPU 2 CPU 2 sends a reschedule IPI to CPU 2 While CPU 3 wakes up, CPU 0 or CPU 1 migrates a waking up task A on CPU 2 CPU 2 finally wakes up, runs task A and discards the Idle Load Balance task A quickly goes back to sleep (before a tick occurs on CPU 2) CPU 2 goes back to idle with NOHZ_BALANCE_KICK set Whenever CPU 2 will be selected as the ILB, no reschedule IPI will be sent because NOHZ_BALANCE_KICK is already set and no Idle Load Balance will be performed. We must wait for the sched softirq to be raised on CPU 2 thanks to another part the kernel to come back to clear NOHZ_BALANCE_KICK. The proposed solution clears NOHZ_BALANCE_KICK in schedule_ipi if we can't raise the sched_softirq for the Idle Load Balance. Change since V1: - move the clear of NOHZ_BALANCE_KICK in got_nohz_idle_kick if the ILB can't run on this CPU (as suggested by Peter) Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1370419991-13870-1-git-send-email-vincent.guittot@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-31sched/fair: Remove unused variable from expire_cfs_rq_runtime()Kamalesh Babulal
Commit 78becc2709 ("sched: Use an accessor to read the rq clock") introduces rq_clock(), which obsoletes the use of the "rq" variable in expire_cfs_rq_runtime() and triggers this build warning: kernel/sched/fair.c: In function 'expire_cfs_rq_runtime': kernel/sched/fair.c:2159:13: warning: unused variable 'rq' [-Wunused-variable] Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Acked-by: Paul Turner <pjt@google.com> Cc: peterz@infradead.org Link: http://lkml.kernel.org/r/1369904660-14169-1-git-send-email-kamalesh@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-31vtime: Use consistent clocks among nohz accountingFrederic Weisbecker
While computing the cputime delta of dynticks CPUs, we are mixing up clocks of differents natures: * local_clock() which takes care of unstable clock sources and fix these if needed. * sched_clock() which is the weaker version of local_clock(). It doesn't compute any fixup in case of unstable source. If the clock source is stable, those two clocks are the same and we can safely compute the difference against two random points. Otherwise it results in random deltas as sched_clock() can randomly drift away, back or forward, from local_clock(). As a consequence, some strange behaviour with unstable tsc has been observed such as non progressing constant zero cputime. (The 'top' command showing no load). Fix this by only using local_clock(), or its irq safe/remote equivalent, in vtime code. Reported-by: Mike Galbraith <efault@gmx.de> Suggested-by: Mike Galbraith <efault@gmx.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28sched: Use swap() macro in scale_stime()Stanislaw Gruszka
Simple cleanup. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Link: http://lkml.kernel.org/r/1367501673-6563-1-git-send-email-sgruszka@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28sched: Use an accessor to read the rq clockFrederic Weisbecker
Read the runqueue clock through an accessor. This prepares for adding a debugging infrastructure to detect missing or redundant calls to update_rq_clock() between a scheduler's entry and exit point. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Turner <pjt@google.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1365724262-20142-6-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28sched: Update rq clock earlier in unthrottle_cfs_rqFrederic Weisbecker
In this function we are making use of rq->clock right before the update of the rq clock, let's just call update_rq_clock() just before that to avoid using a stale rq clock value. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Turner <pjt@google.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1365724262-20142-5-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28sched: Update rq clock before calling check_preempt_curr()Frederic Weisbecker
check_preempt_curr() of fair class needs an uptodate sched clock value to update runtime stats of the current task of the target's rq. When a task is woken up, activate_task() is usually called right before ttwu_do_wakeup() unless the task is still in the runqueue. In the latter case we need to update the rq clock explicitly because activate_task() isn't here to do the job for us. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Turner <pjt@google.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1365724262-20142-4-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28sched: Update rq clock before setting fair group sharesFrederic Weisbecker
Because we may update the execution time in sched_group_set_shares()->update_cfs_shares()->reweight_entity()->update_curr() before reweighting the entity while setting the group shares and this requires an uptodate version of the runqueue clock. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Turner <pjt@google.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1365724262-20142-3-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28sched: Update rq clock before migrating tasks out of dying CPUFrederic Weisbecker
Because the sched_class::put_prev_task() callback of rt and fair classes are referring to the rq clock to update their runtime statistics. There is a missing rq clock update from the CPU hotplug notifier's entry point of the scheduler. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Paul Turner <pjt@google.com> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1365724262-20142-2-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28sched: Remove redundant update_runtime notifierNeil Zhang
migration_call() will do all the things that update_runtime() does. So let's remove it. Furthermore, there is potential risk that the current code will catch BUG_ON at line 689 of rt.c when do cpu hotplug while there are realtime threads running because of enabling runtime twice while the rt_runtime may already changed. Signed-off-by: Neil Zhang <zhangwm@marvell.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1365685499-26515-1-git-send-email-zhangwm@marvell.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28sched/autogroup: Fix race with task_groups listGerald Schaefer
In autogroup_create(), a tg is allocated and added to the task_groups list. If CONFIG_RT_GROUP_SCHED is set, this tg is then modified while on the list, without locking. This can race with someone walking the list, like __enable_runtime() during CPU unplug, and result in a use-after-free bug. To fix this, move sched_online_group(), which adds the tg to the list, to the end of the autogroup_create() function after the modification. Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1369411669-46971-2-git-send-email-gerald.schaefer@de.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-28Merge branch 'sched/cleanups' into sched/coreIngo Molnar
Merge reason: these bits, formerly in sched/urgent, are too late for v3.10. Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-10sched: Use this_rq() helperNathan Zimmer
It is a few instructions more efficent to and slightly more readable to use this_rq()-> instead of cpu_rq(smp_processor_id())-> . Size comparison of kernel/sched/fair.o: text data bss dec hex filename 27972 122 26 28120 6dd8 fair.o.before 27956 122 26 28104 6dc8 fair.o.after Signed-off-by: Nathan Zimmer <nzimmer@sgi.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1368116643-87971-1-git-send-email-nzimmer@sgi.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-07sched: Move update_load_*() methods from sched.h to fair.cPaul Gortmaker
These inlines are only used by kernel/sched/fair.c so they do not need to be present in the main kernel/sched/sched.h file. Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Frederic Weisbecker <fweisbec@gmail.com> Link: http://lkml.kernel.org/r/1366398650-31599-3-git-send-email-paul.gortmaker@windriver.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-07sched: Factor out load calculation code from sched/core.c --> sched/proc.cPaul Gortmaker
This large chunk of load calculation code can be easily divorced from the main core.c scheduler file, with only a couple prototypes and externs added to a kernel/sched header. Some recent commits expanded the code and the documentation of it, making it large enough to warrant separation. For example, see: 556061b, "sched/nohz: Fix rq->cpu_load[] calculations" 5aaa0b7, "sched/nohz: Fix rq->cpu_load calculations some more" 5167e8d, "sched/nohz: Rewrite and fix load-avg computation -- again" More importantly, it helps reduce the size of the main sched/core.c by yet another significant amount (~600 lines). Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Frederic Weisbecker <fweisbec@gmail.com> Link: http://lkml.kernel.org/r/1366398650-31599-2-git-send-email-paul.gortmaker@windriver.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-05-05Merge branch 'timers-nohz-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull 'full dynticks' support from Ingo Molnar: "This tree from Frederic Weisbecker adds a new, (exciting! :-) core kernel feature to the timer and scheduler subsystems: 'full dynticks', or CONFIG_NO_HZ_FULL=y. This feature extends the nohz variable-size timer tick feature from idle to busy CPUs (running at most one task) as well, potentially reducing the number of timer interrupts significantly. This feature got motivated by real-time folks and the -rt tree, but the general utility and motivation of full-dynticks runs wider than that: - HPC workloads get faster: CPUs running a single task should be able to utilize a maximum amount of CPU power. A periodic timer tick at HZ=1000 can cause a constant overhead of up to 1.0%. This feature removes that overhead - and speeds up the system by 0.5%-1.0% on typical distro configs even on modern systems. - Real-time workload latency reduction: CPUs running critical tasks should experience as little jitter as possible. The last remaining source of kernel-related jitter was the periodic timer tick. - A single task executing on a CPU is a pretty common situation, especially with an increasing number of cores/CPUs, so this feature helps desktop and mobile workloads as well. The cost of the feature is mainly related to increased timer reprogramming overhead when a CPU switches its tick period, and thus slightly longer to-idle and from-idle latency. Configuration-wise a third mode of operation is added to the existing two NOHZ kconfig modes: - CONFIG_HZ_PERIODIC: [formerly !CONFIG_NO_HZ], now explicitly named as a config option. This is the traditional Linux periodic tick design: there's a HZ tick going on all the time, regardless of whether a CPU is idle or not. - CONFIG_NO_HZ_IDLE: [formerly CONFIG_NO_HZ=y], this turns off the periodic tick when a CPU enters idle mode. - CONFIG_NO_HZ_FULL: this new mode, in addition to turning off the tick when a CPU is idle, also slows the tick down to 1 Hz (one timer interrupt per second) when only a single task is running on a CPU. The .config behavior is compatible: existing !CONFIG_NO_HZ and CONFIG_NO_HZ=y settings get translated to the new values, without the user having to configure anything. CONFIG_NO_HZ_FULL is turned off by default. This feature is based on a lot of infrastructure work that has been steadily going upstream in the last 2-3 cycles: related RCU support and non-periodic cputime support in particular is upstream already. This tree adds the final pieces and activates the feature. The pull request is marked RFC because: - it's marked 64-bit only at the moment - the 32-bit support patch is small but did not get ready in time. - it has a number of fresh commits that came in after the merge window. The overwhelming majority of commits are from before the merge window, but still some aspects of the tree are fresh and so I marked it RFC. - it's a pretty wide-reaching feature with lots of effects - and while the components have been in testing for some time, the full combination is still not very widely used. That it's default-off should reduce its regression abilities and obviously there are no known regressions with CONFIG_NO_HZ_FULL=y enabled either. - the feature is not completely idempotent: there is no 100% equivalent replacement for a periodic scheduler/timer tick. In particular there's ongoing work to map out and reduce its effects on scheduler load-balancing and statistics. This should not impact correctness though, there are no known regressions related to this feature at this point. - it's a pretty ambitious feature that with time will likely be enabled by most Linux distros, and we'd like you to make input on its design/implementation, if you dislike some aspect we missed. Without flaming us to crisp! :-) Future plans: - there's ongoing work to reduce 1Hz to 0Hz, to essentially shut off the periodic tick altogether when there's a single busy task on a CPU. We'd first like 1 Hz to be exposed more widely before we go for the 0 Hz target though. - once we reach 0 Hz we can remove the periodic tick assumption from nr_running>=2 as well, by essentially interrupting busy tasks only as frequently as the sched_latency constraints require us to do - once every 4-40 msecs, depending on nr_running. I am personally leaning towards biting the bullet and doing this in v3.10, like the -rt tree this effort has been going on for too long - but the final word is up to you as usual. More technical details can be found in Documentation/timers/NO_HZ.txt" * 'timers-nohz-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (39 commits) sched: Keep at least 1 tick per second for active dynticks tasks rcu: Fix full dynticks' dependency on wide RCU nocb mode nohz: Protect smp_processor_id() in tick_nohz_task_switch() nohz_full: Add documentation. cputime_nsecs: use math64.h for nsec resolution conversion helpers nohz: Select VIRT_CPU_ACCOUNTING_GEN from full dynticks config nohz: Reduce overhead under high-freq idling patterns nohz: Remove full dynticks' superfluous dependency on RCU tree nohz: Fix unavailable tick_stop tracepoint in dynticks idle nohz: Add basic tracing nohz: Select wide RCU nocb for full dynticks nohz: Disable the tick when irq resume in full dynticks CPU nohz: Re-evaluate the tick for the new task after a context switch nohz: Prepare to stop the tick on irq exit nohz: Implement full dynticks kick nohz: Re-evaluate the tick from the scheduler IPI sched: New helper to prevent from stopping the tick in full dynticks sched: Kick full dynticks CPU that have more than one task enqueued. perf: New helper to prevent full dynticks CPUs from stopping tick perf: Kick full dynticks CPU if events rotation is needed ...
2013-05-04sched: Keep at least 1 tick per second for active dynticks tasksFrederic Weisbecker
The scheduler doesn't yet fully support environments with a single task running without a periodic tick. In order to ensure we still maintain the duties of scheduler_tick(), keep at least 1 tick per second. This makes sure that we keep the progression of various scheduler accounting and background maintainance even with a very low granularity. Examples include cpu load, sched average, CFS entity vruntime, avenrun and events such as load balancing, amongst other details handled in sched_class::task_tick(). This limitation will be removed in the future once we get these individual items to work in full dynticks CPUs. Suggested-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Christoph Lameter <cl@linux.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kevin Hilman <khilman@linaro.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
2013-05-02Merge branch 'sched-urgent-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler fixes from Ingo Molnar: "This fixes the cputime scaling overflow problems for good without having bad 32-bit overhead, and gets rid of the div64_u64_rem() helper as well." * 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: Revert "math64: New div64_u64_rem helper" sched: Avoid prev->stime underflow sched: Do not account bogus utime sched: Avoid cputime scaling overflow
2013-05-02Merge commit '8700c95adb03' into timers/nohzFrederic Weisbecker
The full dynticks tree needs the latest RCU and sched upstream updates in order to fix some dependencies. Merge a common upstream merge point that has these updates. Conflicts: include/linux/perf_event.h kernel/rcutree.h kernel/rcutree_plugin.h Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
2013-05-01Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs Pull VFS updates from Al Viro, Misc cleanups all over the place, mainly wrt /proc interfaces (switch create_proc_entry to proc_create(), get rid of the deprecated create_proc_read_entry() in favor of using proc_create_data() and seq_file etc). 7kloc removed. * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (204 commits) don't bother with deferred freeing of fdtables proc: Move non-public stuff from linux/proc_fs.h to fs/proc/internal.h proc: Make the PROC_I() and PDE() macros internal to procfs proc: Supply a function to remove a proc entry by PDE take cgroup_open() and cpuset_open() to fs/proc/base.c ppc: Clean up scanlog ppc: Clean up rtas_flash driver somewhat hostap: proc: Use remove_proc_subtree() drm: proc: Use remove_proc_subtree() drm: proc: Use minor->index to label things, not PDE->name drm: Constify drm_proc_list[] zoran: Don't print proc_dir_entry data in debug reiserfs: Don't access the proc_dir_entry in r_open(), r_start() r_show() proc: Supply an accessor for getting the data from a PDE's parent airo: Use remove_proc_subtree() rtl8192u: Don't need to save device proc dir PDE rtl8187se: Use a dir under /proc/net/r8180/ proc: Add proc_mkdir_data() proc: Move some bits from linux/proc_fs.h to linux/{of.h,signal.h,tty.h} proc: Move PDE_NET() to fs/proc/proc_net.c ...
2013-04-30workqueue: include workqueue info when printing debug dump of a worker taskTejun Heo
One of the problems that arise when converting dedicated custom threadpool to workqueue is that the shared worker pool used by workqueue anonimizes each worker making it more difficult to identify what the worker was doing on which target from the output of sysrq-t or debug dump from oops, BUG() and friends. This patch implements set_worker_desc() which can be called from any workqueue work function to set its description. When the worker task is dumped for whatever reason - sysrq-t, WARN, BUG, oops, lockdep assertion and so on - the description will be printed out together with the workqueue name and the worker function pointer. The printing side is implemented by print_worker_info() which is called from functions in task dump paths - sched_show_task() and dump_stack_print_info(). print_worker_info() can be safely called on any task in any state as long as the task struct itself is accessible. It uses probe_*() functions to access worker fields. It may print garbage if something went very wrong, but it wouldn't cause (another) oops. The description is currently limited to 24bytes including the terminating \0. worker->desc_valid and workder->desc[] are added and the 64 bytes marker which was already incorrect before adding the new fields is moved to the correct position. Here's an example dump with writeback updated to set the bdi name as worker desc. Hardware name: Bochs Modules linked in: Pid: 7, comm: kworker/u9:0 Not tainted 3.9.0-rc1-work+ #1 Workqueue: writeback bdi_writeback_workfn (flush-8:0) ffffffff820a3ab0 ffff88000f6e9cb8 ffffffff81c61845 ffff88000f6e9cf8 ffffffff8108f50f 0000000000000000 0000000000000000 ffff88000cde16b0 ffff88000cde1aa8 ffff88001ee19240 ffff88000f6e9fd8 ffff88000f6e9d08 Call Trace: [<ffffffff81c61845>] dump_stack+0x19/0x1b [<ffffffff8108f50f>] warn_slowpath_common+0x7f/0xc0 [<ffffffff8108f56a>] warn_slowpath_null+0x1a/0x20 [<ffffffff81200150>] bdi_writeback_workfn+0x2a0/0x3b0 ... Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Acked-by: Jan Kara <jack@suse.cz> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Dave Chinner <david@fromorbit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-04-30sched: Avoid prev->stime underflowStanislaw Gruszka
Dave Hansen reported strange utime/stime values on his system: https://lkml.org/lkml/2013/4/4/435 This happens because prev->stime value is bigger than rtime value. Root of the problem are non-monotonic rtime values (i.e. current rtime is smaller than previous rtime) and that should be debugged and fixed. But since problem did not manifest itself before commit 62188451f0d63add7ad0cd2a1ae269d600c1663d "cputime: Avoid multiplication overflow on utime scaling", it should be threated as regression, which we can easily fixed on cputime_adjust() function. For now, let's apply this fix, but further work is needed to fix root of the problem. Reported-and-tested-by: Dave Hansen <dave@sr71.net> Cc: <stable@vger.kernel.org> # 3.9+ Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: rostedt@goodmis.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Dave Hansen <dave@sr71.net> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1367314507-9728-3-git-send-email-sgruszka@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-04-30sched: Do not account bogus utimeStanislaw Gruszka
Due to rounding in scale_stime(), for big numbers, scaled stime values will grow in chunks. Since rtime grow in jiffies and we calculate utime like below: prev->stime = max(prev->stime, stime); prev->utime = max(prev->utime, rtime - prev->stime); we could erroneously account stime values as utime. To prevent that only update prev->{u,s}time values when they are smaller than current rtime. Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: rostedt@goodmis.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Dave Hansen <dave@sr71.net> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1367314507-9728-2-git-send-email-sgruszka@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-04-30sched: Avoid cputime scaling overflowStanislaw Gruszka
Here is patch, which adds Linus's cputime scaling algorithm to the kernel. This is a follow up (well, fix) to commit d9a3c9823a2e6a543eb7807fb3d15d8233817ec5 ("sched: Lower chances of cputime scaling overflow") which commit tried to avoid multiplication overflow, but did not guarantee that the overflow would not happen. Linus crated a different algorithm, which completely avoids the multiplication overflow by dropping precision when numbers are big. It was tested by me and it gives good relative error of scaled numbers. Testing method is described here: http://marc.info/?l=linux-kernel&m=136733059505406&w=2 Originally-From: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: rostedt@goodmis.org Cc: Dave Hansen <dave@sr71.net> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20130430151441.GC10465@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-04-30Merge branch 'smp-hotplug-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull SMP/hotplug changes from Ingo Molnar: "This is a pretty large, multi-arch series unifying and generalizing the various disjunct pieces of idle routines that architectures have historically copied from each other and have grown in random, wildly inconsistent and sometimes buggy directions: 101 files changed, 455 insertions(+), 1328 deletions(-) this went through a number of review and test iterations before it was committed, it was tested on various architectures, was exposed to linux-next for quite some time - nevertheless it might cause problems on architectures that don't read the mailing lists and don't regularly test linux-next. This cat herding excercise was motivated by the -rt kernel, and was brought to you by Thomas "the Whip" Gleixner." * 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (40 commits) idle: Remove GENERIC_IDLE_LOOP config switch um: Use generic idle loop ia64: Make sure interrupts enabled when we "safe_halt()" sparc: Use generic idle loop idle: Remove unused ARCH_HAS_DEFAULT_IDLE bfin: Fix typo in arch_cpu_idle() xtensa: Use generic idle loop x86: Use generic idle loop unicore: Use generic idle loop tile: Use generic idle loop tile: Enter idle with preemption disabled sh: Use generic idle loop score: Use generic idle loop s390: Use generic idle loop powerpc: Use generic idle loop parisc: Use generic idle loop openrisc: Use generic idle loop mn10300: Use generic idle loop mips: Use generic idle loop microblaze: Use generic idle loop ...
2013-04-30Merge branch 'sched-core-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler changes from Ingo Molnar: "The main changes in this development cycle were: - full dynticks preparatory work by Frederic Weisbecker - factor out the cpu time accounting code better, by Li Zefan - multi-CPU load balancer cleanups and improvements by Joonsoo Kim - various smaller fixes and cleanups" * 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (45 commits) sched: Fix init NOHZ_IDLE flag sched: Prevent to re-select dst-cpu in load_balance() sched: Rename load_balance_tmpmask to load_balance_mask sched: Move up affinity check to mitigate useless redoing overhead sched: Don't consider other cpus in our group in case of NEWLY_IDLE sched: Explicitly cpu_idle_type checking in rebalance_domains() sched: Change position of resched_cpu() in load_balance() sched: Fix wrong rq's runnable_avg update with rt tasks sched: Document task_struct::personality field sched/cpuacct/UML: Fix header file dependency bug on the UML build cgroup: Kill subsys.active flag sched/cpuacct: No need to check subsys active state sched/cpuacct: Initialize cpuacct subsystem earlier sched/cpuacct: Initialize root cpuacct earlier sched/cpuacct: Allocate per_cpu cpuusage for root cpuacct statically sched/cpuacct: Clean up cpuacct.h sched/cpuacct: Remove redundant NULL checks in cpuacct_acount_field() sched/cpuacct: Remove redundant NULL checks in cpuacct_charge() sched/cpuacct: Add cpuacct_acount_field() sched/cpuacct: Add cpuacct_init() ...
2013-04-29Merge branch 'for-3.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wqLinus Torvalds
Pull workqueue updates from Tejun Heo: "A lot of activities on workqueue side this time. The changes achieve the followings. - WQ_UNBOUND workqueues - the workqueues which are per-cpu - are updated to be able to interface with multiple backend worker pools. This involved a lot of churning but the end result seems actually neater as unbound workqueues are now a lot closer to per-cpu ones. - The ability to interface with multiple backend worker pools are used to implement unbound workqueues with custom attributes. Currently the supported attributes are the nice level and CPU affinity. It may be expanded to include cgroup association in future. The attributes can be specified either by calling apply_workqueue_attrs() or through /sys/bus/workqueue/WQ_NAME/* if the workqueue in question is exported through sysfs. The backend worker pools are keyed by the actual attributes and shared by any workqueues which share the same attributes. When attributes of a workqueue are changed, the workqueue binds to the worker pool with the specified attributes while leaving the work items which are already executing in its previous worker pools alone. This allows converting custom worker pool implementations which want worker attribute tuning to use workqueues. The writeback pool is already converted in block tree and there are a couple others are likely to follow including btrfs io workers. - WQ_UNBOUND's ability to bind to multiple worker pools is also used to make it NUMA-aware. Because there's no association between work item issuer and the specific worker assigned to execute it, before this change, using unbound workqueue led to unnecessary cross-node bouncing and it couldn't be helped by autonuma as it requires tasks to have implicit node affinity and workers are assigned randomly. After these changes, an unbound workqueue now binds to multiple NUMA-affine worker pools so that queued work items are executed in the same node. This is turned on by default but can be disabled system-wide or for individual workqueues. Crypto was requesting NUMA affinity as encrypting data across different nodes can contribute noticeable overhead and doing it per-cpu was too limiting for certain cases and IO throughput could be bottlenecked by one CPU being fully occupied while others have idle cycles. While the new features required a lot of changes including restructuring locking, it didn't complicate the execution paths much. The unbound workqueue handling is now closer to per-cpu ones and the new features are implemented by simply associating a workqueue with different sets of backend worker pools without changing queue, execution or flush paths. As such, even though the amount of change is very high, I feel relatively safe in that it isn't likely to cause subtle issues with basic correctness of work item execution and handling. If something is wrong, it's likely to show up as being associated with worker pools with the wrong attributes or OOPS while workqueue attributes are being changed or during CPU hotplug. While this creates more backend worker pools, it doesn't add too many more workers unless, of course, there are many workqueues with unique combinations of attributes. Assuming everything else is the same, NUMA awareness costs an extra worker pool per NUMA node with online CPUs. There are also a couple things which are being routed outside the workqueue tree. - block tree pulled in workqueue for-3.10 so that writeback worker pool can be converted to unbound workqueue with sysfs control exposed. This simplifies the code, makes writeback workers NUMA-aware and allows tuning nice level and CPU affinity via sysfs. - The conversion to workqueue means that there's no 1:1 association between a specific worker, which makes writeback folks unhappy as they want to be able to tell which filesystem caused a problem from backtrace on systems with many filesystems mounted. This is resolved by allowing work items to set debug info string which is printed when the task is dumped. As this change involves unifying implementations of dump_stack() and friends in arch codes, it's being routed through Andrew's -mm tree." * 'for-3.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq: (84 commits) workqueue: use kmem_cache_free() instead of kfree() workqueue: avoid false negative WARN_ON() in destroy_workqueue() workqueue: update sysfs interface to reflect NUMA awareness and a kernel param to disable NUMA affinity workqueue: implement NUMA affinity for unbound workqueues workqueue: introduce put_pwq_unlocked() workqueue: introduce numa_pwq_tbl_install() workqueue: use NUMA-aware allocation for pool_workqueues workqueue: break init_and_link_pwq() into two functions and introduce alloc_unbound_pwq() workqueue: map an unbound workqueues to multiple per-node pool_workqueues workqueue: move hot fields of workqueue_struct to the end workqueue: make workqueue->name[] fixed len workqueue: add workqueue->unbound_attrs workqueue: determine NUMA node of workers accourding to the allowed cpumask workqueue: drop 'H' from kworker names of unbound worker pools workqueue: add wq_numa_tbl_len and wq_numa_possible_cpumask[] workqueue: move pwq_pool_locking outside of get/put_unbound_pool() workqueue: fix memory leak in apply_workqueue_attrs() workqueue: fix unbound workqueue attrs hashing / comparison workqueue: fix race condition in unbound workqueue free path workqueue: remove pwq_lock which is no longer used ...
2013-04-29fix a leak in /proc/schedstatsAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2013-04-29Merge branch 'core-locking-for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull locking changes from Ingo Molnar: "The most noticeable change are mutex speedups from Waiman Long, for higher loads. These scalability changes should be most noticeable on larger server systems. There are also cleanups, fixes and debuggability improvements." * 'core-locking-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: lockdep: Consolidate bug messages into a single print_lockdep_off() function lockdep: Print out additional debugging advice when we hit lockdep BUGs mutex: Back out architecture specific check for negative mutex count mutex: Queue mutex spinners with MCS lock to reduce cacheline contention mutex: Make more scalable by doing less atomic operations mutex: Move mutex spinning code from sched/core.c back to mutex.c locking/rtmutex/tester: Set correct permissions on sysfs files lockdep: Remove unnecessary 'hlock_next' variable
2013-04-26sched: Fix init NOHZ_IDLE flagVincent Guittot
On my SMP platform which is made of 5 cores in 2 clusters, I have the nr_busy_cpu field of sched_group_power struct that is not null when the platform is fully idle - which makes the scheduler unhappy. The root cause is: During the boot sequence, some CPUs reach the idle loop and set their NOHZ_IDLE flag while waiting for others CPUs to boot. But the nr_busy_cpus field is initialized later with the assumption that all CPUs are in the busy state whereas some CPUs have already set their NOHZ_IDLE flag. More generally, the NOHZ_IDLE flag must be initialized when new sched_domains are created in order to ensure that NOHZ_IDLE and nr_busy_cpus are aligned. This condition can be ensured by adding a synchronize_rcu() between the destruction of old sched_domains and the creation of new ones so the NOHZ_IDLE flag will not be updated with old sched_domain once it has been initialized. But this solution introduces a additionnal latency in the rebuild sequence that is called during cpu hotplug. As suggested by Frederic Weisbecker, another solution is to have the same rcu lifecycle for both NOHZ_IDLE and sched_domain struct. A new nohz_idle field is added to sched_domain so both status and sched_domain will share the same RCU lifecycle and will be always synchronized. In addition, there is no more need to protect nohz_idle against concurrent access as it is only modified by 2 exclusive functions called by local cpu. This solution has been prefered to the creation of a new struct with an extra pointer indirection for sched_domain. The synchronization is done at the cost of : - An additional indirection and a rcu_dereference for accessing nohz_idle. - We use only the nohz_idle field of the top sched_domain. Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: linaro-kernel@lists.linaro.org Cc: peterz@infradead.org Cc: fweisbec@gmail.com Cc: pjt@google.com Cc: rostedt@goodmis.org Cc: efault@gmx.de Link: http://lkml.kernel.org/r/1366729142-14662-1-git-send-email-vincent.guittot@linaro.org [ Fixed !NO_HZ build bug. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
2013-04-24sched: Prevent to re-select dst-cpu in load_balance()Joonsoo Kim
Commit 88b8dac0 makes load_balance() consider other cpus in its group. But, in that, there is no code for preventing to re-select dst-cpu. So, same dst-cpu can be selected over and over. This patch add functionality to load_balance() in order to exclude cpu which is selected once. We prevent to re-select dst_cpu via env's cpus, so now, env's cpus is a candidate not only for src_cpus, but also dst_cpus. With this patch, we can remove lb_iterations and max_lb_iterations, because we decide whether we can go ahead or not via env's cpus. Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Tested-by: Jason Low <jason.low2@hp.com> Cc: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com> Cc: Davidlohr Bueso <davidlohr.bueso@hp.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1366705662-3587-7-git-send-email-iamjoonsoo.kim@lge.com Signed-off-by: Ingo Molnar <mingo@kernel.org>