[alsa-devel] Questions regarding workaround for VMware

[Takashi Iwai]

At Fri, 28 Aug 2009 11:29:52 -0700,
Bankim Bhavsar wrote:
> 
> Takashi I came across a workaround for VMware in ALSA kernel code
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=79452f0a28aa5a40522c487b42a5fc423647ad98
> 
> Thanks for the fix.
> 
> In the comments you mention about inaccurate timer source.
> Could you elaborate on the problem?

The problem is that the irq timing emulated on vmware isn't always
accurate.  The sound hardware is supposed to issue an irq at the
programmed buffer period.  On VMware, this irq generation seems to be
done based on the system timer (or alike), thus it's not generated
at the accurate timing that the hardware should give.

The driver has no idea whether it's on VM, thus assumed that the
IRQ must come accurately more or less.  In the recent code, there are
some additions to correct the DMA position more to believe the accuracy
of the IRQ than the position calculated from the hardware register.
This caused a regression on VMware.  My patch fixed that, at least,
for VMware in the stance of previous versions.

> As of now we see that sound apps running in Fedora 11 guest OS with
> kernel 2.6.29.4-167 don't make any progress and can hang window
> manager like Metacity.
> 
> VMware virtualizes Ensoniq ES1371 sound device.
> 
> Is there something specific you would like us to fix in our virtual
> sound device or timer source?

Well, the only question is how can we get the programmed sound IRQ
more accurately...  If hrtimer with the fine timer source is available,
this could be emulated well, I guess.


thanks,

Takashi