[Intel-gfx] [PATCH 1/2] drm/i915: Keep a count of requests waiting for a slot on GPU

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-11-22 13:31:56)
> 
> On 22/11/2017 12:59, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2017-11-22 12:46:21)
> >> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >>
> >> Keep a per-engine number of runnable (waiting for GPU time) requests.
> >>
> >> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/i915_gem_request.c | 5 +++++
> >>   drivers/gpu/drm/i915/intel_engine_cs.c  | 5 +++--
> >>   drivers/gpu/drm/i915/intel_lrc.c        | 1 +
> >>   drivers/gpu/drm/i915/intel_ringbuffer.h | 8 ++++++++
> >>   4 files changed, 17 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> >> index 7325469ce754..e3c74cafa7d4 100644
> >> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> >> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> >> @@ -480,6 +480,9 @@ void __i915_gem_request_submit(struct drm_i915_gem_request *request)
> >>          engine->emit_breadcrumb(request,
> >>                                  request->ring->vaddr + request->postfix);
> >>   
> >> +       GEM_BUG_ON(engine->queued == 0);
> >> +       engine->queued--;
> > 
> > Ok, so under engine->timeline->lock.
> > 
> >> +
> >>          spin_lock(&request->timeline->lock);
> >>          list_move_tail(&request->link, &timeline->requests);
> >>          spin_unlock(&request->timeline->lock);
> >> @@ -525,6 +528,8 @@ void __i915_gem_request_unsubmit(struct drm_i915_gem_request *request)
> >>          timeline = request->timeline;
> >>          GEM_BUG_ON(timeline == engine->timeline);
> >>   
> >> +       engine->queued++;
> >> +
> >>          spin_lock(&timeline->lock);
> >>          list_move(&request->link, &timeline->requests);
> >>          spin_unlock(&timeline->lock);
> >> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> >> index d53680c08cb0..cc9d60130ddd 100644
> >> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> >> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> >> @@ -1675,12 +1675,13 @@ void intel_engine_dump(struct intel_engine_cs *engine, struct drm_printer *m)
> >>          u64 addr;
> >>   
> >>          drm_printf(m, "%s\n", engine->name);
> >> -       drm_printf(m, "    current seqno %x, last %x, hangcheck %x [%d ms], inflight %d\n",
> >> +       drm_printf(m, "    current seqno %x, last %x, hangcheck %x [%d ms], inflight %d, queued %d\n",
> >>                     intel_engine_get_seqno(engine),
> >>                     intel_engine_last_submit(engine),
> >>                     engine->hangcheck.seqno,
> >>                     jiffies_to_msecs(jiffies - engine->hangcheck.action_timestamp),
> >> -                  engine->timeline->inflight_seqnos);
> >> +                  engine->timeline->inflight_seqnos,
> >> +                  INTEL_GEN(dev_priv) >= 8 ? engine->queued : -1);
> > 
> > Not gen8 specific, just add engine->queued++ to i9xx_submit_request().
> 
> But where to put the decrement, and more importantly, how not make it 
> lag the reality from the retire worker? :(

The decrement is in __i915_gem_request_submit as before.
So basically it should remain 0, since we aren't keeping a queue of work
for the HW and just submitting into the ringbuffer as soon as we are
ready. (This may not always remain so...) Hence why the (last_seqno -
current_seqno) was so important.
-Chris