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From:   Josh Don <joshdon@google.com>
Date:   Mon, 11 Oct 2021 17:14:29 -0700
Message-ID: <CABk29Nt5pcJpbx7mKUfqbf+yahBw3uz50QpBvOm7u3B6uA+AuA@mail.gmail.com>
Subject: Re: [PATCH] sched/core: forced idle accounting
To:     Tao Zhou <tao.zhou@linux.dev>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Vineeth Pillai <vineethrp@gmail.com>,
        Hao Luo <haoluo@google.com>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Sat, Oct 9, 2021 at 11:11 AM Tao Zhou <tao.zhou@linux.dev> wrote:
[snip]
> > +     smt_count = cpumask_weight(smt_mask);
> > +     if (smt_count > 2) {
> > +             unsigned int nr_forced_idle = 0, nr_running = 0;
> > +
> > +             for_each_cpu(i, smt_mask) {
> > +                     rq_i = cpu_rq(i);
> > +                     p = rq_i->core_pick ?: rq_i->curr;
> > +
> > +                     if (p != rq_i->idle)
> > +                             nr_running++;
> > +                     else if (rq_i->nr_running)
> > +                             nr_forced_idle++;
> > +             }
> > +
> > +             if (WARN_ON_ONCE(!nr_running)) {
> > +                     /* can't be forced idle without a running task */
> > +             } else {
> > +                     delta *= nr_forced_idle;
> > +                     delta /= nr_running;
> > +             }
>
> Is it possible to use (smt_count - core_occupation) / core_occupation
> to evaluate this delta ?

Good point, we can use the pre-computed info here. This will help
simplify this logic.

Thanks,
Josh