linux-kernel - Re: [tip:sched/core] sched: Add NEED_RESCHED to the preempt

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Message-ID: <20130927115722.GM3657@laptop.programming.kicks-ass.net>
Date:	Fri, 27 Sep 2013 13:57:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuanhan Liu <yuanhan.liu@...ux.intel.com>
Cc:	mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org,
	Fengguang Wu <fengguang.wu@...el.com>,
	Huang Ying <ying.huang@...el.com>, lkp@...ux.intel.com
Subject: Re: [tip:sched/core] sched: Add NEED_RESCHED to the preempt_count

On Fri, Sep 27, 2013 at 05:14:27PM +0800, Yuanhan Liu wrote:
> On Wed, Sep 25, 2013 at 09:38:38AM -0700, tip-bot for Peter Zijlstra wrote:
> > Commit-ID:  f27dde8deef33c9e58027df11ceab2198601d6a6
> > Gitweb:     http://git.kernel.org/tip/f27dde8deef33c9e58027df11ceab2198601d6a6
> > Author:     Peter Zijlstra <peterz@...radead.org>
> > AuthorDate: Wed, 14 Aug 2013 14:55:31 +0200
> > Committer:  Ingo Molnar <mingo@...nel.org>
> > CommitDate: Wed, 25 Sep 2013 14:07:49 +0200
> > 
> > sched: Add NEED_RESCHED to the preempt_count
> 
> Hi Peter,
> 
> FYI, here we found a pigz regression by this commit.

I just can't help myself; but pigs aren't supposed to fly anyway! :-)

> Here is a list all of changed stats by this commit and it's parent 4a2b4b222743bb07fedf985b884550f2ca067ea9:
> 
> time.involuntary_context_switches                                          [ 3184       - 4753       ]     [ 5.536e+05  - 5.9042e+05 ]
> time.voluntary_context_switches                                            [ 84559      - 1.2223e+05 ]     [ 1.1008e+07 - 1.1092e+07 ]

Gah, that looks like it completely wrecked preemptions.

What kind of PREEMPT Kconfig options do you use? Or rather; could you
attach your .config?
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