[Mesa-dev] [Bug 107670] Massive slowdown under specific memcpy implementations (32bit, no-SIMD, backward copy).

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Fri Aug 24 15:33:35 UTC 2018


--- Comment #7 from iive at yahoo.com ---
(In reply to Grazvydas Ignotas from comment #4)
> What game/benchmark do you see this with?
> Can you try calling _mesa_streaming_load_memcpy() there? It's for reading
> uncached memory, but by the looks of it it might be suitable for writing too.

I'm running Left4Dead2 under wine with Gallium Nine. The game has a `timedemo`
option where it could replay a previously `record`-ed gameplay, so the
benchmark is consistent.
I run it in a window, so I could watch the terminal with `perf top`.
When the problem is present, memcpy() is always the first with 25% usage, while
everything else is less than 2%.
I have to point out that I do run 64bit kernel, I just need the 32 bit
libraries, since the game is 32bit.

_mesa_streaming_load_memcpy() is a little problematic to test, since it is
written in intrinsic and I'm compiling for i486 (that's what my distribution
does). The function also has strong requirement for alignment of both src&dst,
and could fall back to regular memcpy().
Still its existence is proof that there is need for such functionality.

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