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authorPaul E. McKenney <paul.mckenney@linaro.org>2012-02-05 07:42:44 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2012-04-30 10:48:19 -0700
commitcef50120b61c2af4ce34bc165e19cad66296f93d (patch)
tree963a9473155bcf6a8aa12ce92ff842242c9c3575 /kernel/rcutorture.c
parentfae4b54f28f034d228fa3bfc98858c698b64e89c (diff)
rcu: Direct algorithmic SRCU implementation
The current implementation of synchronize_srcu_expedited() can cause severe OS jitter due to its use of synchronize_sched(), which in turn invokes try_stop_cpus(), which causes each CPU to be sent an IPI. This can result in severe performance degradation for real-time workloads and especially for short-interation-length HPC workloads. Furthermore, because only one instance of try_stop_cpus() can be making forward progress at a given time, only one instance of synchronize_srcu_expedited() can make forward progress at a time, even if they are all operating on distinct srcu_struct structures. This commit, inspired by an earlier implementation by Peter Zijlstra (https://lkml.org/lkml/2012/1/31/211) and by further offline discussions, takes a strictly algorithmic bits-in-memory approach. This has the disadvantage of requiring one explicit memory-barrier instruction in each of srcu_read_lock() and srcu_read_unlock(), but on the other hand completely dispenses with OS jitter and furthermore allows SRCU to be used freely by CPUs that RCU believes to be idle or offline. The update-side implementation handles the single read-side memory barrier by rechecking the per-CPU counters after summing them and by running through the update-side state machine twice. This implementation has passed moderate rcutorture testing on both x86 and Power. Also updated to use this_cpu_ptr() instead of per_cpu_ptr(), as suggested by Peter Zijlstra. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Diffstat (limited to 'kernel/rcutorture.c')
-rw-r--r--kernel/rcutorture.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index 8cd262b4149..d10b179dea8 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -639,7 +639,7 @@ static int srcu_torture_stats(char *page)
cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):",
torture_type, TORTURE_FLAG, idx);
for_each_possible_cpu(cpu) {
- cnt += sprintf(&page[cnt], " %d(%d,%d)", cpu,
+ cnt += sprintf(&page[cnt], " %d(%lu,%lu)", cpu,
per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
}