[igt-dev] [PATCH i-g-t] lib/i915: Fix gem_has_execlists to match description

[John Harrison]

On 10/18/2021 00:43, Tvrtko Ursulin wrote:
> On 16/10/2021 00:57, John Harrison wrote:
>> On 10/15/2021 16:39, Dixit, Ashutosh wrote:
>>> On Fri, 15 Oct 2021 16:42:12 -0700, John Harrison wrote:
>>>> On 10/15/2021 16:38, Ashutosh Dixit wrote:
>>>>> Driver is using execlists if it is not using GuC submission.
>>>>> GEM_SUBMISSION_EXECLISTS flag indicates if execlist submission is
>>>>> available, not if it is being used by the driver.
>>>>>
>>>>> Signed-off-by: Ashutosh Dixit <ashutosh.dixit at intel.com>
>>>>> ---
>>>>>    lib/i915/gem_submission.c | 2 +-
>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/lib/i915/gem_submission.c b/lib/i915/gem_submission.c
>>>>> index 2627b802cfb..4312a73bd85 100644
>>>>> --- a/lib/i915/gem_submission.c
>>>>> +++ b/lib/i915/gem_submission.c
>>>>> @@ -153,7 +153,7 @@ bool gem_has_semaphores(int fd)
>>>>>     */
>>>>>    bool gem_has_execlists(int fd)
>>>>>    {
>>>>> -    return gem_submission_method(fd) & GEM_SUBMISSION_EXECLISTS;
>>>>> +    return !gem_has_guc_submission(fd);
>>>> Don't we use ring submission on older platforms?
>>> Hmm, I wasn't aware that there was yet another submission method :/
>>>
>>> So execlist submission is only available for gen >= 8 as the code 
>>> says, in
>>> case anyone knows?
>> Yes. Execlists was new feature of the hardware not all that long ago 
>> (ELSP and all that). Gen8 sounds plausible.
>
> Yes Gen8+.
>
>> Of course, it all depends why the code is asking the question? Does 
>> it really need to know what the submission hardware is? Or is it 
>> actually asking about the scheduling algorithm (as is the case for 
>> gem_exec_fair). Or something else entirely? The scheduler question is 
>> going to change again when we move to using the DRM scheduler instead 
>> of our own private one in the execlist code. Currently though, I 
>> would assume we use the execlist scheduler for ring submission but 
>> certainly not for GuC submission (because the scheduler is in the 
>> hardware).
>
> Nope, no scheduling with ringbuffer backend.
>
> There is I915_PARAM_HAS_SCHEDULER and respective IGT helpers to query 
> what kind of scheduling is supported on the device in question.
>
> It will be on a test per test basis why it is asking the question and 
> what would be the appropriate test.
>
Are you saying that we need to add an extra flag (or even enum field) to 
say what type of scheduler is supported? As in 'fair', 'round robin', 
'DRM', etc.?

I'm not seeing any scheduling _CAP flag that would be relevant to 
differentiating between the GuC and the execlist scheduler implementations.

John.


> Regards,
>
> Tvrtko
>
>>
>> John.
>>
>>>
>>>> Isn't the better fix to just not set the EXECLIST flag when GuC
>>>> submission is detected?
>>> Yes, let me post this patch too. Thanks!
>>