[Bug 87726] [BDW Bisected] OglDrvCtx performance reduced by ~30% after use true PPGTT in Gen8+

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=87726

--- Comment #12 from Eero Tamminen <eero.t.tamminen at intel.com> ---
(In reply to Chris Wilson from comment #11)
> From recollection, OglDrvCtx had perf regressions (and distinct
> rate-limiting steps) in mesa, dri[2,3] and the kernel.

And when run for longer time, also in Unity/compiz (Ubuntu bug tracker has bug
for per-window resource leak which was opened many years ago and still
unfixed).


> It was basically a glClear benchmark across lots of contexts,
> which in many respects shows the same characteristics as lots of clients.

It creates a context, compiles a most trivial shader program, does color buffer
clear, and draws single triangle, swaps it on screen and deletes shaders &
context, on every frame. There's only single context live at any given time
i.e. it simulates lot of successive (windowed & composited) clients, not
parallel ones.

Because it's most trivial use-case possible, and window is fairly small, it's
only partly memory bandwidth (clear) bound.


> That is a level of integration testing above igt.
> Showing the scaling characteristics of the kernel wrt to
> the number of contexts (be they one fd or many) does have coverage in igt.

If you don't think relevant parts of that test couldn't be added to igt, but
you think it's still useful, I think there should be some other open source
implementation for that kind of "stress" test (it should not be left for old
version of Intel *internal* test-suite).

PS. Something I forgot to say earlier.  As we aren't anymore tracking this, I
don't know who will verify the fix.

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