Re: [PATCH v9 15/15] drm/i915: Add deadline based boost support

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

On 03/03/2023 14:48, Rob Clark wrote:
> On Fri, Mar 3, 2023 at 1:58 AM Tvrtko Ursulin
> <tvrtko.ursulin@linux.intel.com> wrote:
>>
>>
>> On 03/03/2023 03:21, Rodrigo Vivi wrote:
>>> On Thu, Mar 02, 2023 at 03:53:37PM -0800, Rob Clark wrote:
>>>> From: Rob Clark <robdclark@chromium.org>
>>>>
>>>
>>> missing some wording here...
>>>
>>>> v2: rebase
>>>>
>>>> Signed-off-by: Rob Clark <robdclark@chromium.org>
>>>> ---
>>>>    drivers/gpu/drm/i915/i915_request.c | 20 ++++++++++++++++++++
>>>>    1 file changed, 20 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
>>>> index 7503dcb9043b..44491e7e214c 100644
>>>> --- a/drivers/gpu/drm/i915/i915_request.c
>>>> +++ b/drivers/gpu/drm/i915/i915_request.c
>>>> @@ -97,6 +97,25 @@ static bool i915_fence_enable_signaling(struct dma_fence *fence)
>>>>       return i915_request_enable_breadcrumb(to_request(fence));
>>>>    }
>>>>
>>>> +static void i915_fence_set_deadline(struct dma_fence *fence, ktime_t deadline)
>>>> +{
>>>> +    struct i915_request *rq = to_request(fence);
>>>> +
>>>> +    if (i915_request_completed(rq))
>>>> +            return;
>>>> +
>>>> +    if (i915_request_started(rq))
>>>> +            return;
>>>
>>> why do we skip the boost if already started?
>>> don't we want to boost the freq anyway?
>>
>> I'd wager Rob is just copying the current i915 wait boost logic.
> 
> Yup, and probably incorrectly.. Matt reported fewer boosts/sec
> compared to your RFC, this could be the bug

Hm, there I have preserved this same !i915_request_started logic.

Presumably it's not just fewer boosts but lower performance. How is he 
setting the deadline? Somehow from clFlush or so?

Regards,

Tvrtko

P.S. Take note that I did not post the latest version of my RFC. The one 
where I fix the fence chain and array misses you pointed out. I did not 
think it would be worthwhile given no universal love for it, but if 
people are testing with it more widely that I was aware perhaps I should.

>>>> +
>>>> +    /*
>>>> +     * TODO something more clever for deadlines that are in the
>>>> +     * future.  I think probably track the nearest deadline in
>>>> +     * rq->timeline and set timer to trigger boost accordingly?
>>>> +     */
>>>
>>> I'm afraid it will be very hard to find some heuristics of what's
>>> late enough for the boost no?
>>> I mean, how early to boost the freq on an upcoming deadline for the
>>> timer?
>>
>> We can off load this patch from Rob and deal with it separately, or
>> after the fact?
> 
> That is completely my intention, I expect you to replace my i915 patch ;-)
> 
> Rough idea when everyone is happy with the core bits is to setup an
> immutable branch without the driver specific patches, which could be
> merged into drm-next and $driver-next and then each driver team can
> add there own driver patches on top
> 
> BR,
> -R
> 
>> It's a half solution without a smarter scheduler too. Like
>> https://lore.kernel.org/all/20210208105236.28498-10-chris@chris-wilson.co.uk/,
>> or if GuC plans to do something like that at any point.
>>
>> Or bump the priority too if deadline is looming?
>>
>> IMO it is not very effective to fiddle with the heuristic on an ad-hoc
>> basis. For instance I have a new heuristics which improves the
>> problematic OpenCL cases for further 5% (relative to the current
>> waitboost improvement from adding missing syncobj waitboost). But I
>> can't really test properly for regressions over platforms, stacks,
>> workloads.. :(
>>
>> Regards,
>>
>> Tvrtko
>>
>>>
>>>> +
>>>> +    intel_rps_boost(rq);
>>>> +}
>>>> +
>>>>    static signed long i915_fence_wait(struct dma_fence *fence,
>>>>                                  bool interruptible,
>>>>                                  signed long timeout)
>>>> @@ -182,6 +201,7 @@ const struct dma_fence_ops i915_fence_ops = {
>>>>       .signaled = i915_fence_signaled,
>>>>       .wait = i915_fence_wait,
>>>>       .release = i915_fence_release,
>>>> +    .set_deadline = i915_fence_set_deadline,
>>>>    };
>>>>
>>>>    static void irq_execute_cb(struct irq_work *wrk)
>>>> --
>>>> 2.39.1
>>>>