[Intel-gfx] [PATCH 1/4] drm/i915/bdw: Clean up execlist queue items in retire_work

[Daniel, Thomas]

> -----Original Message-----
> From: Daniel Vetter [mailto:daniel.vetter at ffwll.ch] On Behalf Of Daniel
> Vetter
> Sent: Monday, November 03, 2014 3:33 PM
> To: Daniel, Thomas
> Cc: intel-gfx at lists.freedesktop.org; shuang.he at linux.intel.com
> Subject: Re: [Intel-gfx] [PATCH 1/4] drm/i915/bdw: Clean up execlist queue
> items in retire_work
> 
> On Wed, Oct 29, 2014 at 09:52:50AM +0000, Thomas Daniel wrote:
> > No longer create a work item to clean each execlist queue item.
> > Instead, move retired execlist requests to a queue and clean up the
> > items during retire_requests.
> >
> > v2: Fix legacy ring path broken during overzealous cleanup
> >
> > v3: Update idle detection to take execlists queue into account
> >
> > Issue: VIZ-4274
> > Signed-off-by: Thomas Daniel <thomas.daniel at intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_gem.c         |    4 +++
> >  drivers/gpu/drm/i915/intel_lrc.c        |   52 ++++++++++++++++++-----------
> --
> >  drivers/gpu/drm/i915/intel_lrc.h        |    2 +-
> >  drivers/gpu/drm/i915/intel_ringbuffer.h |    1 +
> >  4 files changed, 36 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c
> > b/drivers/gpu/drm/i915/i915_gem.c index 827edb5..df28202 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -2718,6 +2718,10 @@ i915_gem_retire_requests(struct drm_device
> *dev)
> >  	for_each_ring(ring, dev_priv, i) {
> >  		i915_gem_retire_requests_ring(ring);
> >  		idle &= list_empty(&ring->request_list);
> > +		if (i915.enable_execlists) {
> > +			idle &= list_empty(&ring->execlist_queue);
> > +			intel_execlists_retire_requests(ring);
> 
> This needs to be the other way round I think - we care about idleness after all
> the currently processed stuff is retired, not before. Otherwise we might
> notice the busy->idle transition one invocation too late.
I thought for a while about this.  The GPU will be idle when the
execlist_queues are empty.
Intel_execlists_retire_requests() cleans up requests which have already
finished so it is more conservative (in terms of CPU idleness) to check the
queue beforehand.  I thought this would be more desirable than
potentially reporting idleness early...
Intel_execlists_retire_requests() can not affect the state of the queue.
And there is no point checking the execlist_retired_req_list because
execlists_retire_requests() always empties it.

Thomas.

> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch