linux-kernel - Re: Fwd: Nice processes prevent frequency increases - possible scheduler regression (known good in 2.6.35)

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Message-ID: <CAKKZj2D-jCkAbEKPX75OFYWrdSYxwh6fFBFy9UBDxy_XHHX3Gg@mail.gmail.com>
Date:	Sat, 3 Nov 2012 16:40:57 +0100
From:	Michal Zatloukal <myxal.mxl@...il.com>
To:	linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org
Subject: Re: Fwd: Nice processes prevent frequency increases - possible
 scheduler regression (known good in 2.6.35)

On Sat, Nov 3, 2012 at 12:48 PM, Mike Galbraith <efault@....de> wrote:
> On Sat, 2012-11-03 at 04:33 -0700, Mike Galbraith wrote:
>> On Fri, 2012-11-02 at 21:09 +0100, Michal Zatloukal wrote:
>>
>> > On the new kernel, the nice processes are never starved - even when
>> > starting a tab-laden chromium session, the processes for BOINC keep
>> > about 20% CPU each (that is normalized to all CPUs, ie 40% nice load
>> > on each core). The problem is, the governor now seems to consider the
>> > non-nice task unable to saturate the CPU, and the cores' frequencies
>> > are hovering between 1.0 and 1.8 GHz. The scheduler keeps scheduling
>> > the nice tasks, and the non-nice tasks are progressing much slower,
>> > caused by the lower CPU speed as well as less processing time
>> > allocated to them. HD video stutters often, and Chromium takes at
>> > least 2-3 times longer to fully load.
>>
>> Your nice 19 tasks receiving 'too much' CPU when there are other
>> runnable tasks around sounds like you have SCHED_AUTOGROUP enabled.
>
> (forgot to mention: if that's the case, you can add noautogroup to your
> kernel command line to turn it off if distro turned it on in .config)
>

Thanks, Ubuntu's kernel is indeed configured with that option enabled,
and passing "noautogroup" at grub restores the previous behaviour. I'm
back to happy days again :) BTW, isn't this the "magic 200-line patch"
I was reading about ~2 years ago?

MZ
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