Messages in this thread Patch in this message | | | From | Wanpeng Li <> | Subject | [PATCH] sched/nohz: Optimize get nohz timer target | Date | Tue, 18 Jun 2019 11:13:01 +0800 |
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From: Wanpeng Li <wanpengli@tencent.com>
On a machine, cpu 0 is used for housekeeping, other 39 cpus are in nohz_full mode. We can observe huge time burn in the loop for seaching nearest busy housekeeper cpu by ftrace.
2) | get_nohz_timer_target() { 2) 0.240 us | housekeeping_test_cpu(); 2) 0.458 us | housekeeping_test_cpu();
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2) 0.292 us | housekeeping_test_cpu(); 2) 0.240 us | housekeeping_test_cpu(); 2) 0.227 us | housekeeping_any_cpu(); 2) + 43.460 us | } This patch optimizes the searching logic by finding a nearest housekeeper cpu in the housekeeping cpumask, it can minimize the worst searching time from ~44us to < 10us in my testing.
Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Wanpeng Li <wanpengli@tencent.com> --- kernel/sched/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 83bd6bb..db550cf 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -548,11 +548,12 @@ int get_nohz_timer_target(void) rcu_read_lock(); for_each_domain(cpu, sd) { - for_each_cpu(i, sched_domain_span(sd)) { + for_each_cpu_and(i, sched_domain_span(sd), + housekeeping_cpumask(HK_FLAG_TIMER)) { if (cpu == i) continue; - if (!idle_cpu(i) && housekeeping_cpu(i, HK_FLAG_TIMER)) { + if (!idle_cpu(i)) { cpu = i; goto unlock; } -- 2.7.4
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