Re: [PATCH] Preemption Latency Measurement Tool

Stefan Westerfeld
2001-09-21T16:31:32Z

Hi!

On Fri, Sep 21, 2001 at 02:42:56AM +0200, Roger Larsson wrote:
> > You might try stracing artsd to see if it hangs at a particular syscall.
> > Use -tt or -r for timestamps and pipe the output through tee (to a file on
> > your ramfs).
>
> I tried playing a mp3 with noatun via artsd. Starting dbench 32 I get the
> same kind of dropouts - and no indication with my latency profiling patch =>
> no process with higher prio is waiting to run!
>
> One of noatun or artsd is waiting for something else! (That is why I included
> Stefan Westerfeld... artsd)
>
> I noticed very nice improvement then reniceing (all) artsd and noatun.
> (I did also change the buffer size in artsd down to 40 ms)
>
> (This part most for Stefan...
> So I thought - lets try to run artsd with RT prio - changed the option
> HOW can it get RT prio when it is not suid? I guess it can not...
>
> So I manually added suid bit - but then noatun could not connect with
> artsd... bug?, backed out the suid change... but is behaves as it works,
> could be that it has so short bursts that prio never get a chance to drop)

If you want to run artsd with RT prio, add suid root to artswrapper if it is
not already there - it should by default, but some distributors/packagers
don't get this right. If you start artsd via kcminit, check the realtime
checkbox, if you do manually, run artswrapper instead of artsd, i.e.

stefan@voyager:~/src/kdelibs/arts$ artswrapper -F10 -S4096
>> running as realtime process now (priority 50)

Artsd itself will not acquire RT prio, only artswrapper will. Noatun doesn't
contain time critical code, so there it doesn't matter.

Cu... Stefan
--
-* Stefan Westerfeld, stefan@space.twc.de (PGP!), Hamburg/Germany
KDE Developer, project infos at http://space.twc.de/~stefan/kde *-