linux-kernel - Re: [ 11/37] sched/nohz: Rewrite and fix load-avg computation -- again

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Message-ID: <20120718001607.GJ25325@burratino>
Date:	Tue, 17 Jul 2012 19:16:07 -0500
From:	Jonathan Nieder <jrnieder@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [ 11/37] sched/nohz: Rewrite and fix load-avg computation --
 again

Hi,

Greg Kroah-Hartman wrote:

> commit 5167e8d5417bf5c322a703d2927daec727ea40dd upstream.
>
> Thanks to Charles Wang for spotting the defects in the current code:
>
>  - If we go idle during the sample window -- after sampling, we get a
>    negative bias because we can negate our own sample.
>
>  - If we wake up during the sample window we get a positive bias
>    because we push the sample to a known active period.
>
> So rewrite the entire nohz load-avg muck once again, now adding
> copious documentation to the code.

I'm thrilled to see this regression fix for stable@, but are we really
really sure that it won't cause new regressions?

Words like "rewrite" set off alarm bells.  As do missing acks:

> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>

(though I guess there's an implied ack from Linus, given that it was
pulled).  And big diffstats:

>  include/linux/sched.h    |    8 +
>  kernel/sched/core.c      |  275 ++++++++++++++++++++++++++++++++++-------------
>  kernel/sched/idle_task.c |    1 
>  kernel/sched/sched.h     |    2 
>  kernel/time/tick-sched.c |    2 
>  5 files changed, 213 insertions(+), 75 deletions(-)

Thanks,
Jonathan
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