linux-kernel - Re: Inconsistent load average on tickless kernels

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Message-ID: <4F958141.2000505@nasza-klasa.pl>
Date:	Mon, 23 Apr 2012 18:20:17 +0200
From:	Lesław Kopeć <leslaw.kopec@...za-klasa.pl>
To:	Jonathan Nieder <jrnieder@...il.com>
CC:	Peter Zijlstra <peterz@...radead.org>, Aman Gupta <aman@...1.net>,
	linux-kernel@...r.kernel.org,
	Chase Douglas <chase.douglas@...onical.com>,
	Damien Wyart <damien.wyart@...e.fr>,
	Kyle McMartin <kyle@...hat.com>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Doug Smythies <dsmythies@...us.net>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Inconsistent load average on tickless kernels

On 04/17/2012 05:30 PM, Jonathan Nieder wrote:

>> Looking at results for 2.6.32.55 branch it seems that we're back at
>> 74f5187ac8 patch - the values are almost the same. The difference
>> between NO_HZ and HZ versions is noticeable.
> 
> How does 3.0.y + c308b56b53 do?  (I ask because the usual flow of
> fixes is mainline -> 3.3.y -> 3.2.y -> 3.0.y -> 2.6.32.y with the
> first three steps happening pretty quickly, so it we can get this
> working on 3.0.y then that would be progress.  Also because, like
> 2.6.32.y, 3.0.y is longterm maintained, so it might be useful in the
> meantime.)

It seems that load reported by 3.0.28 with and without c308b56b53 patch
is almost identical to 3.2.12. This might be more clearly visible on a
comparison chart. [1]

2.6.32.55-hz-0f004f5a69			9.88
2.6.32.55-no-hz-74f5187ac8		2.48
2.6.32.55-no-hz-c308b56b53		2.22
3.0.28-hz				10.66
3.0.28-no-hz				0.60
3.0.28-no-hz-c308b56b53			4.09
3.0.28-no-hz-c308b56b53 nohz=off	6.78
3.2.12-hz				10.16
3.2.12-no-hz				0.66
3.2.12-no-hz-c308b56b53			4.36

What's worth noting is that I haven't seen any nasty side effects of the
latest patch on all kernel versions that I've tested. Hope that helps.


[1] http://img855.imageshack.us/img855/2204/kernelload.png

-- 
Lesław Kopeć


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