Re: [PATCH v2 1/2] sched: force update of blocked load of idle cpus

[Peter Zijlstra]

On Fri, Dec 01, 2017 at 06:01:56PM +0000, Brendan Jackman wrote:
> @@ -8955,8 +8964,20 @@ static void nohz_balancer_kick(void)
>  	if (ilb_cpu >= nr_cpu_ids)
>  		return;
>  
> -	if (test_and_set_bit(NOHZ_BALANCE_KICK, nohz_flags(ilb_cpu)))
> +	if (test_and_set_bit(NOHZ_BALANCE_KICK, nohz_flags(ilb_cpu))) {
> +		if (!only_update) {
> +			/*
> +			 * There's a pending/ongoing nohz kick/balance. If it's
> +			 * just for stats, convert it to a proper load balance.
> +			 */
> +			clear_bit(NOHZ_STATS_KICK, nohz_flags(ilb_cpu));
> +		}
>  		return;
> +	}
> +
> +	if (only_update)
> +		set_bit(NOHZ_STATS_KICK, nohz_flags(ilb_cpu));
> +
>  	/*
>  	 * Use smp_send_reschedule() instead of resched_cpu().
>  	 * This way we generate a sched IPI on the target cpu which

This looks racy.. if its not we don't need atomic ops, if it is but is
still fine it needs a comment.