Re: [RFC] sched: nohz_idle_balance

Peter Zijlstra
2012-09-13T08:20:50Z

On Thu, 2012-09-13 at 06:11 +0200, Vincent Guittot wrote:
> On tickless system, one CPU runs load balance for all idle CPUs.
> The cpu_load of this CPU is updated before starting the load balance
> of each other idle CPUs. We should instead update the cpu_load of the balance_cpu.
>
> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
> ---
> kernel/sched/fair.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1ca4fe4..9ae3a5b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4794,14 +4794,15 @@ static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle)
> if (need_resched())
> break;
>
> - raw_spin_lock_irq(&this_rq->lock);
> - update_rq_clock(this_rq);
> - update_idle_cpu_load(this_rq);
> - raw_spin_unlock_irq(&this_rq->lock);
> + 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);

D'0h good spotting..

> rebalance_domains(balance_cpu, CPU_IDLE);
>
> - rq = cpu_rq(balance_cpu);
> if (time_after(this_rq->next_balance, rq->next_balance))
> this_rq->next_balance = rq->next_balance;
> }