linux-kernel - Re: [RFC PATCH v4 00/19] Core scheduling v4

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Message-ID: <CAERHkruPUrOzDjEp1FV3KY20p9CxLAVzKrZNe5QXsCFZdGskzA@mail.gmail.com>
Date:   Sat, 15 Feb 2020 14:01:36 +0800
From:   Aubrey Li <aubrey.intel@...il.com>
To:     Vineeth Remanan Pillai <vpillai@...italocean.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Dario Faggioli <dfaggioli@...e.com>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v4 00/19] Core scheduling v4

On Fri, Feb 14, 2020 at 11:05 PM Vineeth Remanan Pillai
<vpillai@...italocean.com> wrote:
>
> Hi Aubrey,
>
> Thanks for the updated patches. Merged the changes to our testing branch
> in preparation for v5.
>
>>
>> I added a helper to check task and cpu cookie match, including the
>> entire core idle case. The refined patchset updated at here:
>> https://github.com/aubreyli/linux/tree/coresched_v4-v5.5.2
>
>
> I did not go through all the changes thoroughly, but on a quick glance,
> I feel a small change would optimize it a bit.
>
> +       /*
> +        * A CPU in an idle core is always the best choice for tasks with
> +        * cookies, and ignore cookie match if core scheduler is not enabled
> +        * on the CPU.
> +        */
> +       if (idle_core || !sched_core_enabled(rq))
> +               return true;
> +
> +       return rq->core->core_cookie == p->core_cookie;
> +}
> +
>
> I think check for sched_core_enabled would make sense to be done above the
> for loop. Something like this:
>
> +static inline bool sched_core_cookie_match(struct rq *rq, struct task_struct *p)
> +{
> +       bool idle_core = true;
> +       int cpu;
> +
> +       if (!sched_core_enabled(rq))
> +               return true;
> +
> +       for_each_cpu(cpu, cpu_smt_mask(cpu_of(rq))) {
> +               if (!available_idle_cpu(cpu)) {
> +                       idle_core = false;
> +                       break;
> +               }
> +       }
> +
> +       /*
> +        * A CPU in an idle core is always the best choice for tasks with
> +        * cookies.
> +        */
> +       return idle_core || rq->core->core_cookie == p->core_cookie;
> +}
> +
>
> We can avoid the unnecessary check for idle_core is sched_core is disabled.
> This would optimize in case of systems with lots of cpus.
>
> Please let me know!

Yes, this makes sense, patch updated at here, I put your name there if
you don't mind.
https://github.com/aubreyli/linux/tree/coresched_v4-v5.5.2-rc2

Thanks,
-Aubrey