linux-kernel - Re: Epic regression in throughput since v2.6.23

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Message-ID: <4AA6A9E8.9000407@garzik.org>
Date:	Tue, 08 Sep 2009 15:00:56 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Jesse Brandeburg <jesse.brandeburg@...il.com>
CC:	Serge Belyshev <belyshev@...ni.sinp.msu.ru>,
	Ingo Molnar <mingo@...e.hu>, Con Kolivas <kernel@...ivas.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>
Subject: Re: Epic regression in throughput since v2.6.23

On 09/08/2009 01:47 PM, Jesse Brandeburg wrote:
> On Tue, Sep 8, 2009 at 5:57 AM, Serge
> Belyshev<belyshev@...ni.sinp.msu.ru>  wrote:
>>
>> Hi. I've done measurments of time taken by make -j4 kernel build
>> on a quadcore box.  Results are interesting: mainline kernel
>> has regressed since v2.6.23 release by more than 10%.
>
> Is this related to why I now have to double the amount of threads X I
> pass to make -jX, in order to use all my idle time for a kernel
> compile?  I had noticed (without measuring exactly) that it seems with
> each kernel released in this series mentioned, I had to increase my
> number of worker threads, my common working model now is (cpus * 2) in
> order to get zero idle time.

You will almost certainly see idle CPUs/threads with "make -jN_CPUS" due 
to processes waiting for I/O.

If you're curious, there is also room for experimenting with make's "-l" 
argument, which caps the number of jobs based on load average rather 
than a static number of job slots.

	Jeff


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