[Intel-gfx] [PATCH v6 3/3] drm/i915: Predictive governor to control slice/subslice/eu

[Tvrtko Ursulin]

On 26/11/2019 13:16, Tvrtko Ursulin wrote:
> 
> On 26/11/2019 11:31, Tvrtko Ursulin wrote:
>> On 26/11/2019 11:09, Chris Wilson wrote:
>>> Quoting Tvrtko Ursulin (2019-11-26 10:51:22)
>>>> You mentioned you did some experiment where you did something on 
>>>> context
>>>> pinning and that it did not work so well. I don't know what that was
>>>> though. I don't think that was ever posted?
>>>>
>>>> What I am thinking is this: You drop the timer altogether. Instead in
>>>> __execlists_update_reg_state you look at your gem_context->req_cnt and
>>>> implement your logic there.
>>>
>>> I noticed the same non-sequitur. Except I would push that either the
>>> entire measurement and hence patch series is bogus (beyond the patches
>>> themselves being trivially broken, tested much?), or that it really
>>> should be done from a timer and also adjust pinned contexts ala
>>> reconfigure_sseu.
>>
>> Yeah, if doing it at pin time would not show the power benefit that 
>> would mean looking at req_cnt at pin time does not work, while looking 
>> at it half a timer period ago, on average, works. Which would be very 
>> intriguing. We'd probably want nice graphs in this case overlaying 
>> power, request counts, selected EU config, etc.
> 
> Another thing to try, if simple bucketing of req_cnt to load level at 
> pin time will not work, could be a time-weighted moving average of the 
> same count, but also driven from context pinning.

Yet another interesting experiment would be to try context busyness 
instead of request counts. Crudely, look at context's GPU busy time (I 
have patches for this) per evaluation period and configure accordingly.

This should be able to track better in theory I think, but probably has 
it's own problems. Hard to say without trying and comparing.

Implementation wise, a kthread periodically reconfiguring contexts would 
work I think. Like:

every second
   per context
     query context engine busyness
       calculate relative busyness
         re-configure sseu
		
Regards,

Tvrtko