[Intel-gfx] [PATCH] drm/i915: Allow concurrent read access between CPU and GPU domain

Chris Wilson chris at chris-wilson.co.uk
Tue Apr 10 23:35:19 CEST 2012

On Tue, 10 Apr 2012 11:52:50 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> Similar to allowing a buffer to be simultaneously read by the GPU and
> through the GTT, we wish to allow readback of the pages through the CPU
> domain whilst they are also being read by the GPU. Domain coherency
> is managed by allowing multiple readers, but only a single writer.
> This is used by mesa for its program cache which it may search for every
> new program every frame and then renews should it need to add. During
> renewal, mesa copies the program bo currently executing through a CPU
> mapping onto the new bo. This patch allows the search and that copy to
> proceed without causing a stall on the current batch.

At Daniel's request, I added i-g-t/gem_cpu_concurrent_blit to catch the
possible bugs that may have been introduced by this patch.

Chris Wilson, Intel Open Source Technology Centre

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