On Mon, May 05, 2014 at 11:49:12AM -0700, Ben Widawsky wrote:
> On Mon, May 05, 2014 at 09:07:33AM +0100, Chris Wilson wrote:
> > During the review of
> >
> > commit 1f70999f9052f5a1b0ce1a55aff3808f2ec9fe42
> > Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Date: Mon Jan 27 22:43:07 2014 +0000
> >
> > drm/i915: Prevent recursion by retiring requests when the ring is full
> >
> > Ville raised the point that our interaction with request->tail was
> > likely to foul up other uses elsewhere (such as hang check comparing
> > ACTHD against requests).
> >
> > However, we also need to restore the implicit retire requests that certain
> > test cases depend upon (e.g. igt/gem_exec_lut_handle), this raises the
> > spectre that the ppgtt will randomly call i915_gpu_idle() and recurse
> > back into intel_ring_begin().
>
> Forgive my ignorance. Why is i915_gpu_idle() randomly being called for
> PPGTT? I don't see anything PPGTT specific here.
commit 1f70999f9052f5a1b0ce1a55aff3808f2ec9fe42
Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Date: Mon Jan 27 22:43:07 2014 +0000
drm/i915: Prevent recursion by retiring requests when the ring is full
As the VM do not track activity of objects and instead use a large
hammer to forcibly idle and evict all of their associated objects when
one is released, it is possible for that to cause a recursion when we
need to wait for free space on a ring and call retire requests.
(intel_ring_begin -> intel_ring_wait_request ->
i915_gem_retire_requests_ring -> i915_gem_context_free ->
i915_gem_evict_vm -> i915_gpu_idle -> intel_ring_begin etc)
In order to remove the requirement for calling retire-requests from
intel_ring_wait_request, we have to inline a couple of steps from
retiring requests, notably we have to record the position of the request
we wait for and use that to update the available ring space.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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