[Bug 80705] [IVB/HSW/BYT-M/BDW] GpuTest_v0.5_triangle is slower by 10%~50% in fullscreen than in windowed & composited mode

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=80705

--- Comment #1 from Eero Tamminen <eero.t.tamminen at intel.com> ---
According to Mengmeng, this issue happens only with DRI3, not DRI2.

Can you check with intel_gpu_top (on BYT where it works fine) what is the
"render" value both in fullscreen and windowed mode?

I.e. is GPU 100% utilized in both cases, like it's with DRI2.


FYI: In an unrelated test it was noticed that with DRI3, X still does
occasionally Vsync wait although test had zeroed swap interval.

According to Chris' comment on that test:
---------
The current implementation requires 4 buffers to run the entire pipeline in an
synchronous manner, Keith is only feeding in 3 (from mesa/src/glx/dri3_glx.c)
and so forces the synchronization.
---------

-> With Vsync, test wouldn't be using GPU fully.

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