Re: Very high CPU values in top on idle system (3.0-rc1)

From: Markus Trippelsdorf
Date: Mon May 30 2011 - 16:46:17 EST


On 2011.05.30 at 20:23 +0200, Markus Trippelsdorf wrote:
> On 2011.05.30 at 20:05 +0200, Peter Zijlstra wrote:
> > On Mon, 2011-05-30 at 19:39 +0200, Markus Trippelsdorf wrote:
> > > I get very high CPU values when I run 'top' on my (mostly) idle system
> > > with 3.0-rc1. For example mpd was always in the 1-2% range and is now
> > > constantly over 50%.
> > >
> > > This is caused by:
> > >
> > > commit 317f394160e9beb97d19a84c39b7e5eb3d7815a8
> > > Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > > Date: Tue Apr 5 17:23:58 2011 +0200
> > >
> > > sched: Move the second half of ttwu() to the remote cpu
> > >
> > > When I revert the above I see sane CPU values again.
> >
> > So: echo NO_TTWU_QUEUE > /debug/sched_features, also cures it?
>
> Yes.
>
> > What architecture, what .config, and can you see it with anything other
> > than mpd (yum search mpd, only seems to result in mpd clients not the
> > actual server).
>
> Yes, mpd was just an example. _Every_ program that would normally show in
> the 1-5% CPU range is now in the 30-70% range (X, xterm, etc.).

IOW:

% sudo echo TTWU_QUEUE >| /sys/kernel/debug/sched_features
% top -b -n 1
top - 22:40:38 up 1:46, 11 users, load average: 0.00, 0.02, 0.05
Tasks: 109 total, 1 running, 108 sleeping, 0 stopped, 0 zombie
Cpu(s): 1.0%us, 0.9%sy, 0.0%ni, 98.0%id, 0.1%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 8183132k total, 1365724k used, 6817408k free, 1632k buffers
Swap: 2097148k total, 0k used, 2097148k free, 655208k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
881 mpd 20 0 122m 20m 4832 S 74 0.3 4:25.22 mpd
1564 root 20 0 99428 40m 4716 S 36 0.5 3:36.15 X
1648 markus 20 0 1147m 340m 39m S 16 4.3 1:17.90 firefox-bin
1649 markus 20 0 237m 33m 17m S 6 0.4 1:02.31 konsole

% sudo echo NO_TTWU_QUEUE >| /sys/kernel/debug/sched_features
% top -b -n 1
top - 22:42:07 up 1:48, 11 users, load average: 0.00, 0.01, 0.05
Tasks: 110 total, 1 running, 109 sleeping, 0 stopped, 0 zombie
Cpu(s): 1.0%us, 0.9%sy, 0.0%ni, 98.0%id, 0.1%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 8183132k total, 1377308k used, 6805824k free, 1632k buffers
Swap: 2097148k total, 0k used, 2097148k free, 659896k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1649 markus 20 0 237m 33m 17m S 2 0.4 1:17.69 konsole
1 root 20 0 160 28 12 S 0 0.0 0:16.95 minit
2 root 20 0 0 0 0 S 0 0.0 0:00.36 kthreadd


--
Markus
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