linux-kernel - Re: [PATCH] spin_unlock*_no

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Message-ID: <20130618100541.GN3204@twins.programming.kicks-ass.net>
Date:	Tue, 18 Jun 2013 12:05:41 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] spin_unlock*_no_resched()

On Wed, Jun 12, 2013 at 04:06:47PM +0400, Kirill Tkhai wrote:
> There are many constructions like:
> 
> 	spin_unlock_irq(lock);
> 	schedule();
> 
> In case of preemptible kernel we check if task needs reschedule
> at the end of spin_unlock(). So if TIF_NEED_RESCHED is set
> we call schedule() twice and we have a little overhead here.
> Add primitives to avoid these situations.
> 

Aside from the excellent comments you received from Steven, please also
include a patch that converts some (if not all) of these many callsites
you found so that there's a user of the new code in the kernel.

That way we can simply build + run the kernel and have more confidence
things work as supposed.
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