[Bug 110781] Radeon: heavy r300 performance drop regression between 11.x and 19.x

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=110781

--- Comment #5 from Richard Thier <u9vata@gmail.com> ---
Still fast with mesa 17.2.8 and X.Org X Server 1.19.5

The problem is somewhere between 17.x and 19.x mesa versions (and corresponding
xorg).

Also I have made an strace when it is good in one older system to see number of
CREATE and CLOSE ioctl calls (also the number of CS ioctl calls) are a
magnitude smaller than in case of 19.x!

For example 10-20 seconds of glxgears running leads to 9-10 calls to
DRM_IOCTL_RADEON_GEM_CREATE on mesa 17.2.8 while it leads to 708 (!!!) number
of same calls in the same time period on mesa 19.x! This is surely a quite big
of a difference!

The similar pattern in 17.x is never creating a new gem object:

  ...
  ioctl(6, DRM_IOCTL_RADEON_GEM_WAIT_IDLE, 0xbfcf9f04) = 0 <0.000055>
  ioctl(6, DRM_IOCTL_RADEON_GEM_BUSY, 0xbfcf9d44) = 0 <0.000022>
  ioctl(6, DRM_IOCTL_RADEON_CS, 0xb307d03c) = 0 <0.000089>
  ioctl(6, DRM_IOCTL_RADEON_GEM_WAIT_IDLE, 0xbfcf9f04) = 0 <0.000053>
  ioctl(6, DRM_IOCTL_RADEON_GEM_BUSY, 0xbfcf9d44) = 0 <0.000023>
  ioctl(6, DRM_IOCTL_RADEON_CS, 0xb30910d0) = 0 <0.000095>
  ioctl(6, DRM_IOCTL_RADEON_GEM_WAIT_IDLE, 0xbfcf9f04) = 0 <0.000054>
  ioctl(6, DRM_IOCTL_RADEON_GEM_BUSY, 0xbfcf9d44) = 0 <0.000023>
  ioctl(6, DRM_IOCTL_RADEON_CS, 0xb307d03c) = 0 <0.000090>
  ...

Sometimes when the *_BUSY ioctl call returns -1, it issues a CREATE, but
otherwise not.

I think GEM is some kind of memory handler for the GPU (just like "ttm" in the
perf output) and I think something have messed up with memory handling schemes
for Mobility Radeon 200M (r300) at some mesa update between 17.x and 19.x.

Will try to bisect a closer version as 17.2.8 is from 2017.12.22 in time...

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