[Intel-gfx] [PATCH 3/6] drm/i915/execlists: Force single submission for sentinels

[Tvrtko Ursulin]

On 19/03/2020 15:02, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2020-03-19 14:31:36)
>>
>> On 19/03/2020 09:19, Chris Wilson wrote:
>>> +                             if (has_sentinel(last, rq))
>>>                                        goto done;
>>
>> I am only confused by can_merge_rq saying two sentinel requests can be
>> merged together:
>>
>>          if (unlikely((i915_request_flags(prev) ^ i915_request_flags(next)) &
>>                       (BIT(I915_FENCE_FLAG_NOPREEMPT) |
>>                        BIT(I915_FENCE_FLAG_SENTINEL))))
>>                  return false;
>>
>> What am I missing?
> 
> I thought it was fine to coalesce consecutive sentinels within the
> context into one.
> 
> Except you're thinking about gvt, and not my usage :|

Sentinel is like "only one context in elsp at a time", right? This is 
what GVT wants. And for the active barrier we want single elsp and not 
coalesced with non-sentinel from the same context. But sentinels are 
kernel context, so should be fine. Although it still may be clearer to 
make then not coalesce as well.

Regards,

Tvrtko