Re: [PATCH] drm/i915: Avoid using mappable space for relocation processing through the CPU

[Chris Wilson <chris@chris-wilson.co.uk>]

On Tue, 29 Nov 2011 16:34:41 +0100, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Tue, Nov 29, 2011 at 03:12:40PM +0000, Chris Wilson wrote:
> > We try to avoid writing the relocations through the uncached GTT, if the
> > buffer is currently in the CPU write domain and so will be flushed out to
> > main memory afterwards anyway. Also on SandyBridge we can safely write
> > to the pages in cacheable memory, so long as the buffer is LLC mapped.
> > In either of these caches, we therefore do not need to force the
> > reallocation of the buffer into the mappable region of the GTT, reducing
> > the aperture pressure.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> 
> The error_state capture currently relies on us pinning buffers as mappable
> when they contain relocations (and userspace always submitting a
> batchbuffers containing relocations). You break that guarantee without
> fixing up the error capture code. Otherwise I like this.

I may have sent that patch a little earlier. ;-)
That particular patch stands by itself since we already do use the full
GTT and so need defense against reading through unmappable PTEs because
having some of our errors, you can't be paranoid enough.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre