Re: 2.6 vs 2.4 regression when running gnomemeeting

[Nick Piggin]

Christian Meder wrote:

> On Sat, 2003-12-20 at 03:55, Con Kolivas wrote:
>
> > On Sat, 20 Dec 2003 13:38, Nick Piggin wrote:
> >
> > > Christian Meder wrote:
> > >
> > > > On Sat, 2003-12-20 at 02:26, Nick Piggin wrote:
> > > >
> > > > > Christian Meder wrote:
> > > > >
> > > > > > On Sat, 2003-12-20 at 01:48, Nick Piggin wrote:
> > > > > >
> > > > > > > Sounds reasonable. Maybe its large interrupt or scheduling latency
> > > > > > > caused somewhere else. Does disk activity alone cause a problem?
> > > > > > > find / -type f | xargs cat > /dev/null
> > > > > > > how about
> > > > > > > dd if=/dev/zero of=./deleteme bs=1M count=256
> > > > > > Ok. I've attached the logs from a run with a call with only an
> > > > > > additional dd. The quality was almost undisturbed only very slightly
> > > > > > worse than the unloaded case.
> > Since so many things have actually changed it's going to be hard to extract 
> > what role the cpu scheduler has in this setting, but lets do our best.
> >
> > Is there a reason you're running gnomemeeting niced -10? It is hardly using 
> > any cpu and the problem is actually audio in your case, not the cpu 
> > gnomemeeting is getting. Running dependant things (gnomemeeting, audio 
> > server, gnome etc) at different nice levels is not a great idea as it can 
> > lead to priority inversion scenarios if those apps aren't coded carefully. 
> >
> > What happens if you run gnomemeeting at nice 0?
>
> Exactly the same. It was only reniced to -10 because I tried it and
> forgot to set it back. With your scheduler renicing doesn't make a
> difference. No matter if I renice the compile to 19 or gnomemeeting to
> -10. With Nick's scheduler renicing gnomemeeting to -10 improves the
> situation.

(although not much Con)

> > How is your dma working on your disks?
>
> /dev/hda:
> multcount    =  0 (off)
> IO_support   =  0 (default 16-bit)
> unmaskirq    =  0 (off)
> using_dma    =  1 (on)
> keepsettings =  0 (off)
> readonly     =  0 (off)
> readahead    = 256 (on)
> geometry     = 65535/16/63, sectors = 117210240, start = 0

This might be a problem - try turning unmaskirq on, and possibly
32-bit IO support on (hdparm -u1 -c1 /dev/hda). I think there is
a remote possibility that doing this will corrupt your data just
to let you know.

> > What happens if you don't use an audio server (I'm not sure what the audio 
> > server is in gnome); or if you're not using one what happens when you do?
>
> esd was running but I'm not sure gnomemeeting with ALSA support was
> using it. After killing esd and retrying there was no difference.

So the 1 gnomemeeting process is doing everything? (except display of 
course)

> > Renice the audio server instead?
>
> gnomemeeting without audio server is showing the same phenomenon like
> gnomemeeting with esd.
>
>
> > You've already tried different audio drivers right?
>
> Yes, the phenomenon occurs for the OSS and the ALSA driver.
>
>
> > Nice the compile instead of -nicing the other stuff.
>
> Tried it with same result (see above).
>
>
> > Try the minor interactivity fix I posted only yesterday for different nice 
> > level latencies:
> > http://ck.kolivas.org/patches/2.6/2.6.0/patch-2.6.0-O21int
>
> Actually all the posted results were on a 2.6.0-test11-mm1 with your
> patch added on top. So the patch didn't change anything for me.
>
>
> > Is your network responsible and the audio unrelated? Some have reported 
> > strange problems with ppp or certain network card drivers?
>
> The problem occurs whether I use my WLAN PCMCIA card or my PCMCIA
> Ethernet card.
>
>
> > As you see it's not a straight forward problem but there's some things for you 
> > to get your teeth stuck into. As it stands the cpu scheduler from your top 
> > output appears to be giving appropriate priorities to the different factors 
> > in your equation.
>
> I know that the problem isn't straight forward that's why I refrained a
> long time before posting to linux-kernel trying to rule out different
> scenarios. As it stands I tried different gnomemeeting versions,
> different audio drivers, different nice levels, different schedulers,
> preemption on and off, ACPI on and off, -mm kernels and pristine Linus
> kernels with no luck. If I put CPU load on my box the gnomemeeting
> audiostream gets badly mutilated (unusable). There's not much left I can
> think of that's why I'm finally posting to linux-kernel.

Thanks for your effort.


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