Audio Skips when Scrolling in Firefox

Michel Dänzer michel at
Fri Apr 20 09:54:50 PDT 2007

On Fri, 2007-04-20 at 12:32 -0400, Andrew J. Barr wrote:
> Dave Airlie wrote:
> >> Bah, scrolling in Firefox + Compiz still makes music skip (whereas it
> >> does not in Metacity), but with the aiglx-zero-copy-tfp patches
> >> performance is much improved, notably using the 'scale' (like Apple
> >> Expose) or alt+tab functionality doesn't cause flickering, where it did
> >> before.
> >>
> >> I'm getting there, any suggestions as to what to do about the skipping
> >> or is this even relevant to I should take this problem
> >> elsewhere (e.g. debian-powerpc)?
> >
> > You could profile the system while scrolling and tell us what is
> > taking up all the CPU time..
> This is interesting (see attached). libc6 seems to be eating the lion's
> share of CPU time, I wonder if there are glibc 2.5 issues with ppc. That
> would touch almost everything and explain a lot of issues I've seen.

Doesn't necessarily indicate a problem in glibc, it's probably memcpys
from software rendering.

> Strictly relevant to this list, however, is that a good portion (2nd on
> the list) of the CPU's time while scrolling in Fx is spent in
> in glxFillAlphaChannel.

That means my patches aren't fully effective, as that function is only
called in the !override case. You are using EXA and making sure it has
enough offscreen memory available, aren't you?

Earthling Michel Dänzer           |
Libre software enthusiast         |          Debian, X and DRI developer

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