[Intel-gfx] [RFC 0/8] Force preemption

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-03-22 09:22:55)
> 
> On 21/03/2018 17:26, jeff.mcgee at intel.com wrote:
> > From: Jeff McGee <jeff.mcgee at intel.com>
> > 
> > Force preemption uses engine reset to enforce a limit on the time
> > that a request targeted for preemption can block. This feature is
> > a requirement in automotive systems where the GPU may be shared by
> > clients of critically high priority and clients of low priority that
> > may not have been curated to be preemption friendly. There may be
> > more general applications of this feature. I'm sharing as an RFC to
> > stimulate that discussion and also to get any technical feedback
> > that I can before submitting to the product kernel that needs this.
> > I have developed the patches for ease of rebase, given that this is
> > for the moment considered a non-upstreamable feature. It would be
> > possible to refactor hangcheck to fully incorporate force preemption
> > as another tier of patience (or impatience) with the running request.
> 
> Sorry if it was mentioned elsewhere and I missed it - but does this work 
> only with stateless clients - or in other words, what would happen to 
> stateful clients which would be force preempted? Or the answer is we 
> don't care since they are misbehaving?

They get notified of being guilty for causing a gpu reset; three strikes
and they are out (banned from using the gpu) using the current rules.
This is a very blunt hammer that requires the rest of the system to be
robust; one might argue time spent making the system robust would be
better served making sure that the timer never expired in the first place
thereby eliminating the need for a forced gpu reset.
-Chris