Re: [CFT]: ClangBSD is selfhosting, we need testers now

On Wed, Apr 21, 2010 at 05:23:38PM +0200, Roman Divacky wrote:
> On Wed, Apr 21, 2010 at 05:20:57PM +0200, Alexander Best wrote:
> > i might have stumbled upon a problem with clang. i've compiled a kernel from
> > the clang branch using `make kernel INSTKERNNAME=clang` and booted from it.
> > i'm now experiencing audio problems with mp3s and certain video files.
> > playback is awfully slow and the audio output gets distorted massively. `top`
> > however reports no high cpu load and `vmstat -i` doesn't report anything
> > unusual either.
> > 
> > this problem doesn't occur with a regular gcc-kernel.
> > 
> > both kernels are running under a regular (gcc) world.
> > 
> > i thought it might be a problem with acpi, but disabling acpi
> > (hint.acpi.0.disabled=1) gives me a system freeze.
> 
> I've heard about this problem but did not manage to reproduce that.
> 
> can you try to bisect what file is being miscompiled? ie. compile
> half of the kernel with gcc and half with clang and bisect this
> way to a single file.

The FreeBSD sound subsystem has a sample-rate converter built
into the feeder that (from a cursory look) is probably quite
carefully tweaked to be able to perform well (or at all).  I've
added -multimedia to the CC line, because they're the guys
who are going to know the details.  It's possible that some
GCC-specific manifest constants are being tested-for, with
sub-optimal fall-back code being run, instead.

In the mean-time, Alexander, are there any sound-related sysctls
that you can tweak so that the audio playback that you're doing
does *not* involve sample rate conversion?

Cheers,

-- 
Andrew