linux-kernel - Re: [PATCH 2/7] sched: Add NEED_RESCHED to the preempt

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Message-ID: <CALCETrVU993N6HBkP-G2u-sCu6y6HOp9FknFpah+mpzztE=kkA@mail.gmail.com>
Date:	Wed, 11 Sep 2013 11:07:43 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>, Peter Anvin <hpa@...or.com>,
	Mike Galbraith <bitbucket@...ine.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/7] sched: Add NEED_RESCHED to the preempt_count

On Wed, Sep 11, 2013 at 11:05 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Sep 11, 2013 at 09:35:08AM -0700, Andy Lutomirski wrote:
>> I bet that this improves cross-cpu wakeup latency, too -- the old code
>> would presumably wake up the cpu and then immediately interrupt it.
>
> Yeah,. its what clued Mike in to there being a problem.
>
>> It might be nice to rename one or both of need_resched and
>> test_need_resched, though -- the difference is somewhat inscrutable.
>
> I agreed, I've just been unable to come up with anything sane.
>
> The best I could come up with is renaming
> {set,clear,test}_need_resched() to {}_tif_need_resched(), so we then end
> up with test_tif_need_resched(), which is slightly more different from
> need_resched().

Nothing great.  That's at least better than the current state, I think.

--Andy
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