Re: [Intel-gfx] [PATCH 01/28] drm/i915: Adjust the sentinel assert to match implementation

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

On 09/06/2020 11:47, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2020-06-09 11:39:11)
>>
>> On 09/06/2020 11:29, Chris Wilson wrote:
>>> Quoting Tvrtko Ursulin (2020-06-09 07:59:27)
>>>> 666
>>>> On 08/06/2020 10:33, Chris Wilson wrote:
>>>>> Quoting Tvrtko Ursulin (2020-06-08 08:44:01)
>>>>>>
>>>>>> On 07/06/2020 23:20, Chris Wilson wrote:
>>>>>>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>>>>
>>>>>>> Sentinels are supposed to be last reqeusts in the elsp queue, not the
>>>>>>> only one, so adjust the assert accordingly.
>>>>>>>
>>>>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>>>>>> ---
>>>>>>>      drivers/gpu/drm/i915/gt/intel_lrc.c | 14 +++-----------
>>>>>>>      1 file changed, 3 insertions(+), 11 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
>>>>>>> index d55a5e0466e5..db8a170b0e5c 100644
>>>>>>> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
>>>>>>> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
>>>>>>> @@ -1635,9 +1635,9 @@ assert_pending_valid(const struct intel_engine_execlists *execlists,
>>>>>>>                  ccid = ce->lrc.ccid;
>>>>>>>      
>>>>>>>                  /*
>>>>>>> -              * Sentinels are supposed to be lonely so they flush the
>>>>>>> -              * current exection off the HW. Check that they are the
>>>>>>> -              * only request in the pending submission.
>>>>>>> +              * Sentinels are supposed to be the last request so they flush
>>>>>>> +              * the current exection off the HW. Check that they are the only
>>>>>>> +              * request in the pending submission.
>>>>>>>                   */
>>>>>>>                  if (sentinel) {
>>>>>>>                          GEM_TRACE_ERR("%s: context:%llx after sentinel in pending[%zd]\n",
>>>>>>> @@ -1646,15 +1646,7 @@ assert_pending_valid(const struct intel_engine_execlists *execlists,
>>>>>>>                                        port - execlists->pending);
>>>>>>>                          return false;
>>>>>>>                  }
>>>>>>> -
>>>>>>>                  sentinel = i915_request_has_sentinel(rq);
>>>>>>
>>>>>> FWIW I was changing it to "sentinel |= ..." so it keeps working if we
>>>>>> decide to use more than 2 elsp ports on Icelake one day.
>>>>>
>>>>> But it will always fail on the next port...
>>>>
>>>> I don't follow. Sentinel has to be last so if it fails on the next port
>>>> it is correct to do so, no?
>>>
>>> Exactly. We only check the first port after setting sentinel, if that
>>> port is occupied we fail. Hence why we don't need |=, since there is no
>>> continuation.
>>
>> But if more than two ports we also overwrite the bools so: sentinel,
>> non-sentinel, sentinel would not catch. I was just future proofing it. :)
> 
> [0] -> sentinel
> [1] != NULL -> ERROR
> 
> [0] -> not sentinel
> [1] -> sentinel
> [2] != NULL -> ERROR
> 
> We fail if anything comes after a sentinel.

:) Joke is on me.

Regards,

Tvrtko
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