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 11:29, 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. :)

Regards,

Tvrtko
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