linux-kernel - Re: [PATCH 1/7] x86/fpu: Simplify the fpu->last_cpu logic and rename it to fpu->fpregs

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Date:   Thu, 26 Jan 2017 08:51:27 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Rik van Riel <riel@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH 1/7] x86/fpu: Simplify the fpu->last_cpu logic and rename
 it to fpu->fpregs_cached

On Thu, Jan 26, 2017 at 6:54 AM, Rik van Riel <riel@...hat.com> wrote:
> On Thu, 2017-01-26 at 12:26 +0100, Ingo Molnar wrote:
>
>> index c56fb57f2991..7eb2f3041fde 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -1253,6 +1253,8 @@ void set_task_cpu(struct task_struct *p,
>> unsigned int new_cpu)
>>                       p->sched_class->migrate_task_rq(p);
>>               p->se.nr_migrations++;
>>               perf_event_task_migrate(p);
>> +
>> +             arch_task_migrate(p);
>>       }
>>
>
> Does it really count as a "simplification" if you add a
> scheduler callback?
>
> This code does not seem any easier to understand than
> the old code...

I think I lean toward liking Ingo's version better.  The old code most
likely saved an instruction, but the new code gets the point across
quite nicely.