[Intel-gfx] [PATCH] drm/i915: Do not add an interrupt for a context switch

[Daniel Vetter]

On Thu, Aug 8, 2013 at 1:25 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Thu, Aug 08, 2013 at 01:18:18AM +0200, Daniel Vetter wrote:
>> Afaict the request holds a ref on the context, and that a ref on the hw
>> context bo. But the active list itself (thanks to the move_to_active)
>> should also hold a ref to the hw context bo, so I don't think we really
>> need full request here. The old context might disappear, but no one really
>> cares if it disappears a notch too early since the backing storage will
>> survive long enough.
>
> The next request holds a ref to the new context. We care about holding a
> ref to the old context until the hw has finished writing to it. That is
> the purpose of taking a request here, to bump the old_ctx->bo->active
> for the context save. Otherwise the backing storage is liable to disappear
> too early (and the hw write to a random location).

Hm, I might be especially dense, but doesn't the
i915_gem_object_move_to_active(from->obj, ring) call right above the
add_request take care of exactly that, whether we have the request
added or not? And anyone waiting for that object (e.g. the eviction
code) will notice in check_olr that the request is missing, add it and
then wait for it?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch