Messages in this thread | | | Date | Fri, 4 Sep 2015 11:56:33 -0400 | From | Luiz Capitulino <> | Subject | Re: [PATCH 1/2] nohz: Affine unpinned timers to housekeepers |
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On Tue, 1 Sep 2015 22:47:24 +0200 Frederic Weisbecker <fweisbec@gmail.com> wrote:
> On Tue, Sep 01, 2015 at 07:14:13PM +0000, Jiang, Yunhong wrote: > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > > index 8b864ec..0902e4d 100644 > > > --- a/kernel/sched/core.c > > > +++ b/kernel/sched/core.c > > > @@ -623,18 +623,21 @@ int get_nohz_timer_target(void) > > > int i, cpu = smp_processor_id(); > > > struct sched_domain *sd; > > > > > > - if (!idle_cpu(cpu)) > > > + if (!idle_cpu(cpu) && is_housekeeping_cpu(cpu)) > > > return cpu; > > > > > > rcu_read_lock(); > > > for_each_domain(cpu, sd) { > > > for_each_cpu(i, sched_domain_span(sd)) { > > > - if (!idle_cpu(i)) { > > > + if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) { > > > > Hi, Frederic, sorry for a naive question. Per my understanding, the tick_nohz_full_mask is added to cpu_isolated_map in > > sched_init_smp(), and the cpu_isolated_map is excluded from sched_domain in init_sched_domains(), so why check here? > > Very good observation! But it's better to keep this check in the domain loop in > case things change in the future such as removing that cpu_isolated_map inclusion > or other suprises.
I have another observation.
As nohz_full cores are already excluded from the sched domains, this patch boils down to migrating timers which are queued by the nohz_full core itself. However, it only fully works for lowres timers. hrtimers may still fire on nohz_full cores, because hrtimers are only migrated if the core returned by get_nohz_timer_target() has a queued timer expiring before than the timer being migrated.
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