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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 22/11/2017 12:59, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2017-11-22 12:46:21)
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> Keep a per-engine number of runnable (waiting for GPU time) requests.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@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? :(

Regards,

Tvrtko
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