[Intel-gfx] [PATCH] drm/i915: Park the GPU on module load

[Tvrtko Ursulin]

On 14/09/2018 10:47, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2018-09-14 10:40:43)
>>
>> On 14/09/2018 09:34, Chris Wilson wrote:
>>> Once we have flushed the first request through the system to both load a
>>> context and record the default state; tell the GPU to park and idle
>>> itself, putting itself immediately (hopefully at least) into a
>>> powersaving state, and allowing ourselves to start from known state
>>> after setting up all our bookkeeping.
>>
>> Otherwise this would happen after a second or so, when the idle work
>> handler does it. Crucial thing to mention is I think the park/unpark
>> cycle which sets up the pinned default state.
> 
> Hmm, I didn't think it was worth highlight it here as one assumes that
> all the bookkeeping is equally required :) I pulled out for special
> mention in the comment, because I thought that was relevant to the
> function where we are acquiring the default_state.
>   
>> Alternative to patch could be to extract
>> __intel_engine_pin_default_state to be called from here and from
>> intel_engines_unpark.
>>
>> But I guess there is some value in going powersave as soon as possible
>> so okay.
> 
> Yeah. Later on (as in patches that have been on the ml for several
> months with feature requests depending on them...) we acquire a
> load_powersaving_context() function, which should make this a little more
> interesting.
> 
>>> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>>> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>> ---
>>>    drivers/gpu/drm/i915/i915_gem.c | 8 ++++++++
>>>    1 file changed, 8 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>>> index 89834ce19acd..be9d012d851b 100644
>>> --- a/drivers/gpu/drm/i915/i915_gem.c
>>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>>> @@ -5414,6 +5414,14 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
>>>    
>>>        assert_kernel_context_is_current(i915);
>>>    
>>> +     /*
>>> +      * Immediately park the GPU so that we enable powersaving and
>>> +      * treat it as idle. The next time we issue a request, we will
>>> +      * unpark and start using the engine->pinned_default_state, otherwise
>>> +      * it is in limbo and an early reset may fail.
>>> +      */
>>> +     __i915_gem_park(i915);
>>
>> Why not after we have grabbed the default state?
> 
> I was just wanting to tie it to the switch to kernel-context + idle.
> I was thinking this was the closed point to the normal park sequence.
>   
>> I was worried this might access a sleeping device but apparently at
>> least vma unbind takes the rpm ref. Still, just this I think makes it
>> more logical to park after we have grabbed the default state, instead o
>> putting the device to sleep and then immediately waking up below.
> 
> Oh, we have wakerefs aplenty on module load, we are not assuming gt.awake
> here.

Now I am having doubts if it is a business of 
__intel_engines_record_defaults to park the engines, or the caller 
(i915_gem_init) would be a better design..

Regards,

Tvrtko