Commit-ID: ed61bbc69c773465782476c7e5869fa5607fa73a Gitweb: http://git.kernel.org/tip/ed61bbc69c773465782476c7e5869fa5607fa73a Author: Tim Chen <[email protected]> AuthorDate: Tue, 20 May 2014 14:39:27 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Thu, 5 Jun 2014 11:52:01 +0200
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 <[email protected]> Acked-by: Russ Anderson <[email protected]> Reviewed-by: Rik van Riel <[email protected]> Reviewed-by: Jason Low <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Len Brown <[email protected]> Cc: Dimitri Sivanich <[email protected]> Cc: Hedi Berriche <[email protected]> Cc: Andi Kleen <[email protected]> Cc: MichelLespinasse <[email protected]> Cc: Peter Hurley <[email protected]> Cc: Linus Torvalds <[email protected]> Link: http://lkml.kernel.org/r/1400621967.2970.280.camel@schen9-DESK Signed-off-by: Ingo Molnar <[email protected]> --- 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 b71d8c3..7a0c000 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
