[Bug 36596] Major 2D performance bottleneck (most noticeable with compiz)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=36596

--- Comment #4 from Jason Cassell <bluesloth600 at gmail.com> 2011-04-28 16:36:31 PDT ---
(In reply to comment #3)
> Does that involve wobbly windows or any other effects?

It's the same problem with and without wobbly windows.

One thing I noticed with wobbly windows is that sometimes (but not every time)
when the framerate goes back to normal, they'll wobble very fast, like they're
trying to "catch up".  It looks like it's trying to render all the frames, but
some of them just show up late, like something got delayed in a buffer
somewhere.  I only notice that with wobbly windows, but that might just be
because the wobbling makes the phenomenon easier to see.

> Did you double-check that enabling LLVM actually worked?

The configure script output says it's using llvm, and "llvm" appears a lot in
the build log.  I don't know if there's anything else to check.

> If that's not the problem, and if the slowness coincides with high CPU usage, a
> profile from sysprof or oprofile might give some ideas.

The slowness coincides with very low CPU usage.  According to htop, when it's
working fine, compiz uses from 5% to 16% CPU to move windows around, depending
on the window and whether they're wobbly.  When it's slow, compiz's CPU usage
is 0.0%, and the CPU usage of everything else combined is less than 2%.

This is on a dual core 2 GHz CPU, probably throttled back to 800 Mhz, but I
don't know for sure because I wasn't running conky.

htop refreshed every 2 seconds.  Sometimes a refresh would make compiz freeze
for a fraction of a second, but most of them didn't.

Would it be useful to profile something anyway?

BTW, I should have mentioned that I have to boot with the "noirqdebug" kernel
parameter, otherwise the kernel will sometimes disable the Radeon's IRQ saying
"irq 19: nobody cared" (the exact message is no longer in the logs).  Once the
IRQ was disabled, everything still worked, but more slowly.

I also have scrolling performance problems in compiz, but compiz is infamous
for causing things like that, so I'm guessing it's a different bug, and I'll
worry about it later.

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