[Mesa-dev] [PATCH 7/7] i965: Drop non-LLC lunacy in the program cache code.

[Kenneth Graunke]

On Saturday, July 22, 2017 2:14:28 AM PDT Chris Wilson wrote:
> Quoting Kenneth Graunke (2017-07-22 00:17:47)
> > The non-LLC story was a horror show.  We uploaded data via pwrite
> > (drm_intel_bo_subdata), which would stall if the cache BO was in
> > use (being read) by the GPU.  Obviously, we wanted to avoid that.
> > So, we tried to detect whether the buffer was busy, and if so, we'd
> > allocate a new BO, map the old one read-only (hopefully not stalling),
> > copy all shaders compiled since the dawn of time to the new buffer,
> > upload our new one, toss the old BO, and let the state upload code
> > know that our program cache BO changed.  This was a lot of extra data
> > copying, and flagging BRW_NEW_PROGRAM_CACHE would also cause a new
> > STATE_BASE_ADDRESS to be emitted, stalling the entire pipeline.
> > 
> > Not only that, but our rudimentary busy tracking consistented of a flag
> > set at execbuf time, and not cleared until we threw out the program
> > cache BO.  So, the first shader upload after any drawing would hit this
> > "abandon the cache and start over" copying path.
> > 
> > This is largely unnecessary - it's just ancient and crufty code.  We can
> > use the same persistent mapping paths on all platforms.  On non-ancient
> > kernels, this will use a write combining map, which should be reasonably
> > fast.
> > 
> > One aspect that is worse: we do occasionally grow the program cache BO,
> > and copy the old contents to the newer BO.  This will suffer from UC
> > readback performance now.  To mitigate this, we use the MOVNTDQA based
> > streaming memcpy on platforms with SSE 4.1 (all Gen7+ atoms).  Gen4-5
> > are unfortunately going to be penalized.
> > 
> > v2: Add MOVNTDQA path, rebase on other map flag changes.
> 
> Don't forgot cache->bo_used_by_gpu!

Right!  fixed locally, thanks!
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