On 20 December 2017 at 15:03, Peter Zijlstra <pet...@infradead.org> wrote:
> 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.
NOHZ_STATS_KICK modification is protected by test_and_set_bit(NOHZ_BALANCE_KICK.
You're right that we don't need atomics ops and __set_bit() is enough
