[Intel-gfx] [PATCH 03/15] drm/i915: Only spin whilst waiting on the current request

Chris Wilson chris at chris-wilson.co.uk
Tue Dec 1 07:58:27 PST 2015

On Tue, Dec 01, 2015 at 03:47:34PM +0000, Dave Gordon wrote:
> On 30/11/15 10:06, Tvrtko Ursulin wrote:
> >
> >On 29/11/15 08:48, Chris Wilson wrote:
> >>Limit busywaiting only to the request currently being processed by the
> >>GPU. If the request is not currently being processed by the GPU, there
> >>is a very low likelihood of it being completed within the 2 microsecond
> >>spin timeout and so we will just be wasting CPU cycles.
> >>
> >>v2: Check for logical inversion when rebasing - we were incorrectly
> >>checking for this request being active, and instead busywaiting for
> >>when the GPU was not yet processing the request of interest.
> >>
> >>v3: Try another colour for the seqno names.
> >>v4: Another colour for the function names.
> Adding a field in the request to track the sequence number of the
> previous request isn't ideal when considering the scheduler and
> preemption. But we've got a separate batch-in-progress sequence
> number in the hardware status page (also for use by TDR to check
> which batch is currently running), so you could use that. Then the
> check is simply

As demonstrated TDR doesn't need it, and the GPU scheduler has to fix up
the seqno anyway to maintain retirement order of the request list.

Chris Wilson, Intel Open Source Technology Centre

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