linux-kernel - Re: printk timestamps jumping back and forth in 2.6.25-rc.

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Date:	Sat, 1 Mar 2008 03:59:53 +0300
From:	"Alexey Zaytsev" <alexey.zaytsev@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Thomas Gleixner" <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>,
	"Arjan van de Ven" <arjan@...ux.intel.com>
Subject: Re: printk timestamps jumping back and forth in 2.6.25-rc.

On Sat, Mar 1, 2008 at 3:42 AM, Alexey Zaytsev <alexey.zaytsev@...il.com> wrote:
>
> On Fri, Feb 29, 2008 at 10:45 PM, Ingo Molnar <mingo@...e.hu> wrote:
>  >
>  >  * Alexey Zaytsev <alexey.zaytsev@...il.com> wrote:
>  >
>  >
>  >
>  > > On Thu, Feb 28, 2008 at 11:16 PM, Ingo Molnar <mingo@...e.hu> wrote:
>  >  > >
>  >  > >  * Ingo Molnar <mingo@...e.hu> wrote:
>  >  > >
>  >  > >  > > Anything else I can do?
>  >  > >  >
>  >  > >  > yes, please test the patch below - does it fix the problem?
>  >  >
>  >  > The patch worked well, thanks
>  >  >
>  >  > I still observe some uneven mouse behaviour during compilations (linux
>  >  > kernel, make -j 6), like, when I slowly move the mouse, it would stop
>  >  > for a split of a second every few seconds (the intervals are not
>  >  > equal). On 2.6.23/24 it works very smooth. Of course, I can't say that
>  >  > the scheduler is to be blamed. It was only my assumption because I
>  >  > thought I might be confused by the non-monotinic time, which I see is
>  >  > not the case. Any ideas, how to debug this?
>  >
>  >  could you try latencytop, what does it say, what type of scheduler (and
>  >  other) delays are there?
>  >
>
>  I'm not sure I fully understand how to use this tool.
>  There are clearly two possible options to the utility,
>  --unknown and -d, but I still have no idea what they do..
>
>  Does the latencytop-0.3 actually work? I my case the upper half of the
>  window is always empty. The lower half shows always one line, like
>
>  Scheduler: waiting for cpu \t \t \t \t $some_val $some_val
>
>  The two values are always identical.
>
>  In the 2.6.24 case, the values for Xorg are always around 20 ms
>  when a make -j 6 is runig in parallel. For the 2.6.25 the
>  values jump from 100 ms to over 1000 ms.
>
>  Later I mounted a tmpfs and run the compilation (from root) there
>  (swap turned off). This time the Xorg latency was usually less then
>  30 ms, but the gnome-terminal (running from an other user) was not
>  that lucky with latencies around 500-1000 ms. Now I ran the same compilation
>  from user, and the latencies came back to what I observed before, with
>  gnome-terminal being about 30-50 and Xorg jumping from 100 to now
>  over 2000. The latencytop and some daemons runnig as different users
>  also had comparable latencyes.
>
>  Yes, fair group scheduler enabled, the config can be seen here:
>  http://romomatic.osuosl.org/share/xl0/config-2.6.25-rc3
>
>  I"ll now recompile with fair group scheduler disabled, just to be sure.
>

Yes, with the group scheduler disabled, the latencies for both Xorg and
gnome-terminal do net exceed 15 ms. And the mouse is also smooth.
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