Re: 2.6 vs 2.4 regression when running gnomemeeting

From: Nick Piggin
Date: Fri Dec 19 2003 - 19:51:52 EST




Christian Meder wrote:

On Sat, 2003-12-20 at 01:21, Nick Piggin wrote:

Christian Meder wrote:


On Fri, 2003-12-19 at 21:32, William Lee Irwin III wrote:


On Fri, Dec 19, 2003 at 09:11:50PM +0100, Christian Meder wrote:


I've got a longstanding regression in gnomemeeting usage when switching
between 2.4 and 2.6 kernels.
Phenomenon: Without load gnomemeeting VOIP connections are fine. As soon as some
load like a kernel compile is put on the laptop the gnomemeeting audio
stream is cut to pieces and gets unintelligible . On 2.4.2x I don't get
even the slightest distortion in the audio stream under load. I played
around with different nice levels with no success. The problem persisted
during the whole 2.6.0-test series no matter whether I used -mm kernels
or pristine Linus kernels. Even when nicing the kernel compile to +19
the distortions start right away. I tried Nick Piggin's scheduler which
fared slightly better after changing the nice level of gnomemeeting to
-10 but it's still a far cry from the 2.4.2x feeling without any
fiddling with nice values.
Any hints where to start looking are greatly appreciated.


Please instrument your workload with the following, and send logs of the
output (preferably compressed) to me and possibly others:

top b d 5
vmstat 5
while true; do cat /proc/vmstat; sleep 5; done
while true; do cat /proc/meminfo; sleep 5; done

A good way to log commands like this is:

(command) > /home/foo.log.1 2>&1 &

where parentheses surround the command in the actual shell input.


Hi,

I've attached the tarred output of a gnomemeeting run without load and
without distortions and another tarred output of a gnomemeeting run
while compiling a kernel with severe distortions in the audio stream.


You're getting a lot fewer interrupts in the loaded case. Maybe its
the sound card driver that has the regression from 2.4? It could be
that 2.6 allows a smaller sound fragment size which is more stressful.



Well I had the same problem with the OSS driver on 2.6. Now I use the
ALSA driver because I thought that could possibly improve things. The
ALSA driver is better indeed but it doesn't change this particular
phenomenon. Additionally I'd guess that the latest ALSA driver in 2.4
and 2.6 doesn't differ significantly and 2.4.2x with the latest ALSA
works great while 2.6 doesn't.



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

You said it faired slightly better with my scheduler when renicing
gnome meeting to -10. How much better is that?

whats your /proc/cpuinfo?


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