[Bug 101769] 2X performance regression on Mesa 17.1 vs 17.0

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101769

            Bug ID: 101769
           Summary: 2X performance regression on Mesa 17.1 vs 17.0
           Product: Mesa
           Version: 17.1
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: major
          Priority: medium
         Component: Drivers/Gallium/radeonsi
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: david at lunarg.com
        QA Contact: dri-devel at lists.freedesktop.org

Created attachment 132646
  --> https://bugs.freedesktop.org/attachment.cgi?id=132646&action=edit
hack to apitrace for duplicating problem

We have an internal OpenGL benchmarking tool that measures the performance of
certain frames in apitrace files. We have been using this tool to measure
the performance of various releases of Mesa.

We recently found a large regression in Mesa performance of Half Life Episode
2, as measured by our benchmarking tool. We measured the following frame rates
when running the benchmark with Mesa built from the listed source tags:

    tag mesa-17.0.0   358.6 fps
    tag mesa-17.1.3   151.1 fps

This is a reduction in performance of more than 2X.

Since the tool we use to measure performance is an internal tool and we cannot
distribute it, I hacked apitrace to behave similar to our tool so that apitrace
can be used to measure the performance of the problem frame.  The frame rates I
measured with this hacked apitrace benchmark are:

    tag mesa-17.0.0   417.7 fps
    commit 071d80b    393.9 fps
    commit f81ede4    324.6 fps
    tag mesa-17.1.3   196.0 fps

The hacked apitrace shows about the same performance drop between mesa-17.0.0
and mesa-17.1.3 as our original benchmark. I also include the results for
commits 071d80b and f81ede4 because commit f81ede4 seemed to show the single
largest performance drop of all commits between mesa-17.0.0 and mesa-17.1.3.

The configuration of the system I have been using to measure Mesa performance
is:

   CPU: Intel(R) Core(TM) i5-6600K CPU @ 3.50GHz
   RAM: 16Gb
   GPU: AMD RX480

Attached is the patch I applied to apitrace to create my hacked apitrace that
attempts to duplicate the original benchmark.

After building apitrace with the above patch, I used the following command to
measure performance:

    vblank_mode=0 glretrace -b hl2_linux.trace

I can make the hl2_linux.trace trace file available on request. We cannot
widely distribute it because it contains Valve IP (i.e. game images). Please
send a request directly to david at lunarg.com.

Note that we have observed similar performance drops for other games, but I
have concentrated on isolating and reporting on one frame in one game for now.

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