Subject: Re: 2.6.14-rc5-rt3 - `IRQ 8'[798] is being piggy
From: Lee Revell <rlrevell@joe-job.com>
To: Mark Knecht <markknecht@gmail.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>
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Date: Fri, 21 Oct 2005 15:44:42 -0400
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On Fri, 2005-10-21 at 11:52 -0700, Mark Knecht wrote:
> On 10/21/05, Lee Revell <rlrevell@joe-job.com> wrote:
> > On Fri, 2005-10-21 at 10:40 -0700, Mark Knecht wrote:
> > > On 10/21/05, Mark Knecht <markknecht@gmail.com> wrote:
> > > > Hi,
> > > >    Maybe I'm catching something here? Maybe not - no xruns as of yet,
> > > > but I've never seen these messages before. Kernel config attached.
> > > >
> > > >    dmesg has filled up with these messages:
> > > >
> >
> > This isn't a real problem.  You enabled CONFIG_RTC_HISTOGRAM.  Don't do
> > that.
> >
> > Lee
> 
> 
> Right, but the 'piggy' messages are a real prblem, aren't they?

No I don't think so.  CONFIG_RTC_HISTOGRAM is a hack, designed to work
with a specific test program that runs SCHED_FIFO and poll()s on the
RTC.  VLC apparently poll()s on the RTC but does not run SCHED_FIFO.  So
of course there will be delays.

Now that the kernel has good soft realtime support and non-root RT
scheduling, these apps really need to adopt a correct soft RT design
like JACK.  AFAICT they don't even bother to try to get SCHED_FIFO for
the time-sensitive rendering threads.  I can't even get totem-xine (the
default "Sound and Movie Player" for Gnome) to keep the audio and video
in sync.  mplayer only plays smoothly if I run it at nice -10.  Etc.

The Linux kernel is pretty good for RT these days but compared to OSX or
even Windows the apps are a joke.

Lee

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