On Wed, 7 Jun 2006, Barry Scott wrote:
Mark Vojkovich wrote:
On Tue, 6 Jun 2006, Barry Scott wrote:
I'm seeing the X process take a lot more CPU time to run any workload in
1280x768 compared to a standard VGA mode like 1280x1024.
For example running a text scrolling app (lots of XCopyArea calls) I see
the
following CPU usage figures:
1280x1024: 6.75%
1280x768: 10.53%
top shows that the X process is the only one to show a change between
the two modes.
With XVIDEO apps the difference is from 50% to 70% to play a movie.
This happens with the i810 driver and the via driver so I don't think
its a driver
specific issue. I think that X is changing its behavior.
I seriously doubt that.
Is it possible that X has turned off it acceleration in 1280x768 mode?
X doesn't have anything to do with acceleration. This is entirely
a driver/HW issue.
I'm surprised that XAA has nothing to do with the X core. I'd have assumed
that if the driver supports a speed up then X uses it otherwise X falls
back to
none accelerated algorithm. But if you say its all in the driver I guess
that
means that both the via and the i810 driver have the same bug in them.
It's not clear that it's a bug yet.
What can I look at to find out what the problem is?
Is your refresh rate the same in both cases? Integrated
graphics have peculiar performance characteristics because the
graphics hardware shares memory bandwidth with the CPU.
Refresh rate is 60Hz in both cases. So I assume that its not a memory
bandwidth change as you suggest.
Where should I look to get some data to work on?
When you did your text scrolling test, were the windows the same
size? It's often the case that the CPU usage increases when the
graphics speed is faster. That's because the faster graphics allows
more work to get done. If it takes a certain amount of CPU to render
one line of text and scroll the window, faster scrolling (because you
have few lines to scroll) translates to higher CPU usage.
Run some experiments on fixed size windows.
x11perf -scroll500 would be an interesting test. Ideally both
resolutions would have the same performance and CPU usage. If
the lower resolution runs faster, which it might due to more
memory bandwidth being available, then I'd expect CPU usage to
increase as well.
Mark.
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