From ed61bbc69c773465782476c7e5869fa5607fa73a Mon Sep 17 00:00:00 2001 From: Tim Chen Date: Tue, 20 May 2014 14:39:27 -0700 Subject: [PATCH] sched/balancing: Reduce the rate of needless idle load balancing The current no_hz idle load balancer do load balancing for *all* idle cpus, even though the time due to load balance for a particular idle cpu could be still a while in the future. This introduces a much higher load balancing rate than what is necessary. The patch changes the behavior by only doing idle load balancing on behalf of an idle cpu only when it is due for load balancing. On SGI's systems with over 3000 cores, the cpu responsible for idle balancing got overwhelmed with idle balancing, and introduces a lot of OS noise to workloads. This patch fixes the issue. Signed-off-by: Tim Chen Acked-by: Russ Anderson Reviewed-by: Rik van Riel Reviewed-by: Jason Low Signed-off-by: Peter Zijlstra Cc: Andrew Morton Cc: Len Brown Cc: Dimitri Sivanich Cc: Hedi Berriche Cc: Andi Kleen Cc: MichelLespinasse Cc: Peter Hurley Cc: Linus Torvalds Link: http://lkml.kernel.org/r/1400621967.2970.280.camel@schen9-DESK Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index b71d8c39f1fd..7a0c000b6005 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7193,12 +7193,17 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) rq = cpu_rq(balance_cpu); - raw_spin_lock_irq(&rq->lock); - update_rq_clock(rq); - update_idle_cpu_load(rq); - raw_spin_unlock_irq(&rq->lock); - - rebalance_domains(rq, CPU_IDLE); + /* + * If time for next balance is due, + * do the balance. + */ + if (time_after_eq(jiffies, rq->next_balance)) { + raw_spin_lock_irq(&rq->lock); + update_rq_clock(rq); + update_idle_cpu_load(rq); + raw_spin_unlock_irq(&rq->lock); + rebalance_domains(rq, CPU_IDLE); + } if (time_after(this_rq->next_balance, rq->next_balance)) this_rq->next_balance = rq->next_balance; -- 2.45.2