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

Alexey Zaytsev
2008-03-01T01:00:10Z

On Sat, Mar 1, 2008 at 3:42 AM, Alexey Zaytsev <alexey.zaytsev@gmail.com> wrote:
>
> On Fri, Feb 29, 2008 at 10:45 PM, Ingo Molnar <mingo@elte.hu> wrote:
> >
> > * Alexey Zaytsev <alexey.zaytsev@gmail.com> wrote:
> >
> >
> >
> > > On Thu, Feb 28, 2008 at 11:16 PM, Ingo Molnar <mingo@elte.hu> wrote:
> > > >
> > > > * Ingo Molnar <mingo@elte.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.