[Intel-gfx] [PATCH 1/2] drm/i915/gt: Try to smooth RPS spikes

[Chris Wilson]

Quoting Andi Shyti (2020-04-15 11:56:59)
> Hi Chris,
> 
> On Tue, Apr 14, 2020 at 05:14:22PM +0100, Chris Wilson wrote:
> > By the time we respond to the RPS interrupt [inside a worker], the GPU
> > may be running a different workload. As we look to make the evalution
> > intervals shorter, these spikes are more likely to okay. Let's try to
> > smooth over the spikes in the workload by comparing the EI interrupt
> > [up/down events] with the most recently completed EI; if both say up,
> > then increase the clocks, if they disagree stay the same. In principle,
> > this means we now take 2 up EI to go increase into the next bin, and
> > similary 2 down EI to decrease. However, if the worker runs fast enough,
> > the previous EI in the registers will be the same as triggered the
> > interrupt, so responsiveness remains unaffect. [Under the current scheme
> > where EI are on the order of 10ms, it is likely that this is true and we
> > compare the interrupt with the EI that caused it.]
> 
> looks reasonable to me. Wouldn't it make also sense to evaluate
> the difference between the current and the previous pm_iir?

I was considering it... We can't look at IIR since we apply the mask,
but ISR should be valid. Worth a looksee.
-Chris