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

[Chris Wilson]

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

-- 
Chris Wilson, Intel Open Source Technology Centre