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

[John Harrison]

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.

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).

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!