[alsa-devel] PCM multi A/V Sync bug on SMP system

Keith Chew keith.chew at gmail.com
Wed Apr 28 22:12:33 CEST 2010

> I would like to help out in fixing this, but need a little bit of
> guidance from the experts here. Have I identified the problem
> correctly? Ie interaction between "multi" and "dmix" on a 5.1 channel
> card giving timing issues on an SMP system? If it is unlikely, I will
> investigate other areas.

Ok, I don't seem to be getting much help from this mailing list, so I
have dug deeper into the code, and found the problem. In
pcm_dmix_i386.c, we have:

				if (!strncmp(line, "processor", 9))

I have commented out the smp++, so that it thinks that I am on a uni
processor. Voila, so AV sync issues!

My question now is what are the implications of this change? Looking
at pcm_dmix_i386.h, it uses locks on an SMP system, but exclude them
if not SMP. Do we still need this lock, even if I am on a dual core,
ie 1 processor 2 cores?

I have CC'ed the author of the file, Jaroslav Kysela.


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