linux-kernel - Re: [PATCH 4/4] nohz: Convert a few places to use local per cpu accesses

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Message-ID: <20130816161954.GA32704@redhat.com>
Date:	Fri, 16 Aug 2013 18:19:54 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Fernando Luis Vazquez Cao <fernando_b1@....ntt.co.jp>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH 4/4] nohz: Convert a few places to use local per cpu
	accesses

On 08/16, Peter Zijlstra wrote:
>
> OK so these patches look ok to me -- didn't read in detail though.
>
> On Fri, Aug 16, 2013 at 05:42:33PM +0200, Frederic Weisbecker wrote:
> > A few functions use remote per CPU access APIs when they
> > deal with local values.
> >
> > Just to the right conversion to improve performance, code
> > readability and debug checks.
>
> > @@ -410,7 +408,7 @@ static void tick_nohz_update_jiffies(ktime_t now)
> >
> >  static void tick_nohz_stop_idle(int cpu, ktime_t now)
> >  {
> > -	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
> > +	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
>
> What's there from stopping someone from calling this with cpu !=
> smp_processor_id() ?

I _guess_ this should not happen, but in this case we should probably
remove the "cpu" argument. And smp_processor_id() in tick_nohz_idle_exit().

tick_check_idle/tick_check_nohz doesn't need "int cpu" too, it seems.

Oleg.

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