linux-kernel - Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

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Date:	Wed, 21 Aug 2013 19:09:27 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	Fernando Luis Vázquez Cao 
	<fernando_b1@....ntt.co.jp>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock

On 08/21, Peter Zijlstra wrote:
>
> On Wed, Aug 21, 2013 at 01:35:51PM +0200, Oleg Nesterov wrote:
> >
> > Well, the only overhead is "if(to == MAX_SCHEDULE_TIMEOUT)" at the start.
> > I don't think it makes sense to copy-and-paste the identical code to
> > avoid it. But please ignore, this is really minor and off-topic.
>
> Ah, so the 'problem' is that schedule_timeout() doesn't live in
> kernel/sched/core.c and we thus get an extra function call (which are
> somewhat expensive on some archs).

So, unlike me, you like -02 more than -Os ;)

> +static inline long schedule_timeout(long timeout)
> +{
> +	if (timeout == MAX_SCHEDULE_TIMEOUT) {
> +		schedule();
> +		return timeout;
> +	}
> +	return __schedule_timeout(timeout);
> +}

Well this means that every caller will do the MAX_SCHEDULE_TIMEOUT
check inline, and this case is unlikely. And you are also going
to make  schedule_timeout_*() inline...

But,

> +static inline long schedule_timeout_interruptible(long timeout)
> +{
> +	__set_current_state(TASK_INTERRUPTIBLE);
> +	return schedule_timeout(timeout);
> +}
> +static inline long schedule_timeout_killable(long timeout)
> +{
> +	__set_current_state(TASK_KILLABLE);
> +	return schedule_timeout(timeout);
> +}
> +static inline long schedule_timeout_uninterruptible(long timeout)
> +{
> +	__set_current_state(TASK_UNINTERRUPTIBLE);
> +	return schedule_timeout(timeout);
> +}
> ...
> -signed long __sched schedule_timeout_interruptible(signed long timeout)
> -{
> -	__set_current_state(TASK_INTERRUPTIBLE);
> -	return schedule_timeout(timeout);
> -}
> -EXPORT_SYMBOL(schedule_timeout_interruptible);
> -
> -signed long __sched schedule_timeout_killable(signed long timeout)
> -{
> -	__set_current_state(TASK_KILLABLE);
> -	return schedule_timeout(timeout);
> -}
> -EXPORT_SYMBOL(schedule_timeout_killable);
> -
> -signed long __sched schedule_timeout_uninterruptible(signed long timeout)
> -{
> -	__set_current_state(TASK_UNINTERRUPTIBLE);
> -	return schedule_timeout(timeout);
> -}
> -EXPORT_SYMBOL(schedule_timeout_uninterruptible);
> +EXPORT_SYMBOL(__schedule_timeout);

personally I think this particular change is fine.

Or we can export a single schedule_timeout_state(timeout, state) to
factor out get_current().

But just in case, of course I won't argue in any case.

Oleg.

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