From 69f7c0a1be84b10a81b6edcce2dbee0cdec26eba Mon Sep 17 00:00:00 2001 From: Con Kolivas Date: Mon, 5 Mar 2007 00:30:29 -0800 Subject: [PATCH] sched: remove SMT nice Remove the SMT-nice feature which idles sibling cpus on SMT cpus to facilitiate nice working properly where cpu power is shared. The idling of cpus in the presence of runnable tasks is considered too fragile, easy to break with outside code, and the complexity of managing this system if an architecture comes along with many logical cores sharing cpu power will be unworkable. Remove the associated per_cpu_gain variable in sched_domains used only by this code. Also: The reason is that with dynticks enabled, this code breaks without yet further tweaks so dynticks brought on the rapid demise of this code. So either we tweak this code or kill it off entirely. It was Ingo's preference to kill it off. Either way this needs to happen for 2.6.21 since dynticks has gone in. Signed-off-by: Con Kolivas Acked-by: Ingo Molnar Cc: Nick Piggin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/sched.c | 155 +-------------------------------------------------------- 1 file changed, 1 insertion(+), 154 deletions(-) (limited to 'kernel') diff --git a/kernel/sched.c b/kernel/sched.c index 5f102e6c7a4..a4ca632c477 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -3006,23 +3006,6 @@ static inline void idle_balance(int cpu, struct rq *rq) } #endif -static inline void wake_priority_sleeper(struct rq *rq) -{ -#ifdef CONFIG_SCHED_SMT - if (!rq->nr_running) - return; - - spin_lock(&rq->lock); - /* - * If an SMT sibling task has been put to sleep for priority - * reasons reschedule the idle task to see if it can now run. - */ - if (rq->nr_running) - resched_task(rq->idle); - spin_unlock(&rq->lock); -#endif -} - DEFINE_PER_CPU(struct kernel_stat, kstat); EXPORT_PER_CPU_SYMBOL(kstat); @@ -3239,10 +3222,7 @@ void scheduler_tick(void) update_cpu_clock(p, rq, now); - if (p == rq->idle) - /* Task on the idle queue */ - wake_priority_sleeper(rq); - else + if (p != rq->idle) task_running_tick(rq, p); #ifdef CONFIG_SMP update_load(rq); @@ -3251,136 +3231,6 @@ void scheduler_tick(void) #endif } -#ifdef CONFIG_SCHED_SMT -static inline void wakeup_busy_runqueue(struct rq *rq) -{ - /* If an SMT runqueue is sleeping due to priority reasons wake it up */ - if (rq->curr == rq->idle && rq->nr_running) - resched_task(rq->idle); -} - -/* - * Called with interrupt disabled and this_rq's runqueue locked. - */ -static void wake_sleeping_dependent(int this_cpu) -{ - struct sched_domain *tmp, *sd = NULL; - int i; - - for_each_domain(this_cpu, tmp) { - if (tmp->flags & SD_SHARE_CPUPOWER) { - sd = tmp; - break; - } - } - - if (!sd) - return; - - for_each_cpu_mask(i, sd->span) { - struct rq *smt_rq = cpu_rq(i); - - if (i == this_cpu) - continue; - if (unlikely(!spin_trylock(&smt_rq->lock))) - continue; - - wakeup_busy_runqueue(smt_rq); - spin_unlock(&smt_rq->lock); - } -} - -/* - * number of 'lost' timeslices this task wont be able to fully - * utilize, if another task runs on a sibling. This models the - * slowdown effect of other tasks running on siblings: - */ -static inline unsigned long -smt_slice(struct task_struct *p, struct sched_domain *sd) -{ - return p->time_slice * (100 - sd->per_cpu_gain) / 100; -} - -/* - * To minimise lock contention and not have to drop this_rq's runlock we only - * trylock the sibling runqueues and bypass those runqueues if we fail to - * acquire their lock. As we only trylock the normal locking order does not - * need to be obeyed. - */ -static int -dependent_sleeper(int this_cpu, struct rq *this_rq, struct task_struct *p) -{ - struct sched_domain *tmp, *sd = NULL; - int ret = 0, i; - - /* kernel/rt threads do not participate in dependent sleeping */ - if (!p->mm || rt_task(p)) - return 0; - - for_each_domain(this_cpu, tmp) { - if (tmp->flags & SD_SHARE_CPUPOWER) { - sd = tmp; - break; - } - } - - if (!sd) - return 0; - - for_each_cpu_mask(i, sd->span) { - struct task_struct *smt_curr; - struct rq *smt_rq; - - if (i == this_cpu) - continue; - - smt_rq = cpu_rq(i); - if (unlikely(!spin_trylock(&smt_rq->lock))) - continue; - - smt_curr = smt_rq->curr; - - if (!smt_curr->mm) - goto unlock; - - /* - * If a user task with lower static priority than the - * running task on the SMT sibling is trying to schedule, - * delay it till there is proportionately less timeslice - * left of the sibling task to prevent a lower priority - * task from using an unfair proportion of the - * physical cpu's resources. -ck - */ - if (rt_task(smt_curr)) { - /* - * With real time tasks we run non-rt tasks only - * per_cpu_gain% of the time. - */ - if ((jiffies % DEF_TIMESLICE) > - (sd->per_cpu_gain * DEF_TIMESLICE / 100)) - ret = 1; - } else { - if (smt_curr->static_prio < p->static_prio && - !TASK_PREEMPTS_CURR(p, smt_rq) && - smt_slice(smt_curr, sd) > task_timeslice(p)) - ret = 1; - } -unlock: - spin_unlock(&smt_rq->lock); - } - return ret; -} -#else -static inline void wake_sleeping_dependent(int this_cpu) -{ -} -static inline int -dependent_sleeper(int this_cpu, struct rq *this_rq, struct task_struct *p) -{ - return 0; -} -#endif - #if defined(CONFIG_PREEMPT) && defined(CONFIG_DEBUG_PREEMPT) void fastcall add_preempt_count(int val) @@ -3507,7 +3357,6 @@ need_resched_nonpreemptible: if (!rq->nr_running) { next = rq->idle; rq->expired_timestamp = 0; - wake_sleeping_dependent(cpu); goto switch_tasks; } } @@ -3547,8 +3396,6 @@ need_resched_nonpreemptible: } } next->sleep_type = SLEEP_NORMAL; - if (rq->nr_running == 1 && dependent_sleeper(cpu, rq, next)) - next = rq->idle; switch_tasks: if (next == rq->idle) schedstat_inc(rq, sched_goidle); -- cgit v1.2.3-70-g09d2