[Bug 26599] torcs performance regression (git 47136fa)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=26599

--- Comment #11 from Dave Witbrodt <dawitbro at sbcglobal.net> 2010-05-12 18:12:32 PDT ---
[Hmmm, I replied via email yesterday, but apparently that didn't work... since
nothing appeared here in 24 hours.]

For the record, this bug was about the "vline" feature in the radeon driver,
and 'torcs' was merely the metric being used to identify and measure the impact
it had on performance.

Regarding closing the bug:  I assumed that the developers would close the "bug"
after Alex identified (in comment #2) that the problem was caused by vline...
and it was actually a feature, not a bug.

When the bug was NOT closed by any developer, I assumed (maybe wrongly?) that
the impact of vline (versus radeon with vline removed) was still of some
interest.  As a result, I began reporting my results once or twice a month of
testing my latest radeon update from git with and without the vline feature.


In hindsight, I think this was not a bug; it was true that when vline was first
introduced that the 'torcs' track I use for testing went from playable to
unplayable.  Vline does cause a decrease in max frame rate, but something else
got fixed (who knows what?  DRM?  Mesa?) which rendered 'torcs' playable even
with vline.


I sympathize with AttilaN, though:  one of the programs I use for testing
OpenGL performance (prboom) has suffered a horrible performance regression
since January or February.  The problem is, I've only been testing 'prboom'
using one map which doesn't expose the regression.  I accidentally played
another map a few days ago -- previously perfectly playable -- which was now
experiencing performance issues that made it difficult or impossible to play.

Wanting to report a bug, I tried a great variety of older packages (from
Debian, and locally built from git) -- Linux kernels/DRM, radeon drivers, Mesa
libraries, libdrm, X servers -- going as far back as the beginning of March.  I
was not able to find a combination of old software that made the performance
regression disappear.

At this point, I'm totally baffled:  I don't know when the problems were
introduced, or in what software.  I also just discovered that a different track
in 'torcs' only allows me 5 frames per second (on HD 4850 hardware!), even with
vline removed from radeon.  I'm afraid I can't locate the cause of these
regressions, and for now have given up trying.  I guess all I can do is hope
the developers are seeing the same problems, and are able to find fixes or
workarounds.

None of this has much to do with vline, though.  If a developer closes this
bug, I will understand.  If not, I will continue to report here what
performance differences I'm seeing in the radeon driver with and without the
vline feature.


Thanks,
Dave W.

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