linux-kernel - Re: [RFC PATCH 06/23] sched/core: Update the classification of the current task

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Date:   Fri, 16 Sep 2022 07:51:01 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [RFC PATCH 06/23] sched/core: Update the classification of the
 current task

On Sat, Sep 10, 2022 at 03:21:20PM +0800, Hillf Danton wrote:
> On 9 Sep 2022 16:11:48 -0700 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com> wrote:
> > @@ -5445,6 +5445,9 @@ void scheduler_tick(bool user_tick)
> >  	unsigned long thermal_pressure;
> >  	u64 resched_latency;
> >  
> > +	if (sched_task_classes_enabled() && user_tick)
> > +		arch_update_task_class(curr, is_core_idle(cpu));
> > +
> >  	arch_scale_freq_tick();
> >  	sched_clock_tick();
> 
Thank you very much for your feedback Hillf!

> Given user_tick == true, core is not idle regardless of SMT.
> IOW I doubt is_core_idle() helps here.

Perhaps is_core_idle() is a bad name? The second argument of arch_update_
task_class() is smt_siblings_idle. is_core_idle() gives us the answer
we want.

is_core_idle() only checks the siblings of @cpu. It explicitly skips itself
from the checks of idle state. We are only interested in the idle state of
the siblings.

Am I missing anything?

Thanks and BR,
Ricardo