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 <tim.c.chen@linux.intel.com> Acked-by: Russ Anderson <rja@sgi.com> Reviewed-by: Rik van Riel <riel@redhat.com> Reviewed-by: Jason Low <jason.low2@hp.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Len Brown <len.brown@intel.com> Cc: Dimitri Sivanich <sivanich@sgi.com> Cc: Hedi Berriche <hedi@sgi.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: MichelLespinasse <walken@google.com> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/1400621967.2970.280.camel@schen9-DESK Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -7193,12 +7193,17 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
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rq = cpu_rq(balance_cpu);
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rq = cpu_rq(balance_cpu);
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raw_spin_lock_irq(&rq->lock);
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/*
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update_rq_clock(rq);
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* If time for next balance is due,
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update_idle_cpu_load(rq);
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* do the balance.
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raw_spin_unlock_irq(&rq->lock);
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*/
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if (time_after_eq(jiffies, rq->next_balance)) {
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rebalance_domains(rq, CPU_IDLE);
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raw_spin_lock_irq(&rq->lock);
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update_rq_clock(rq);
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update_idle_cpu_load(rq);
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raw_spin_unlock_irq(&rq->lock);
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rebalance_domains(rq, CPU_IDLE);
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}
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if (time_after(this_rq->next_balance, rq->next_balance))
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if (time_after(this_rq->next_balance, rq->next_balance))
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this_rq->next_balance = rq->next_balance;
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this_rq->next_balance = rq->next_balance;
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