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

From: Andy Lutomirski <luto@amacapital.net>
To: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: Re: [PATCH 1/7] x86/fpu: Simplify the fpu->last_cpu logic and rename it to fpu->fpregs_cached
Date: Thu, 26 Jan 2017 08:51:27 -0800	[thread overview]
Message-ID: <CALCETrU=3DpMsOAki2kcfQ+8KUvHm1LnVs1yr7424q7H-dL6ww@mail.gmail.com> (raw)
In-Reply-To: <1485442458.15964.50.camel@redhat.com>

On Thu, Jan 26, 2017 at 6:54 AM, Rik van Riel <riel@redhat.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.