[Intel-gfx] [PATCH] drm/i915: Replace hangcheck by heartbeats

[Chris Wilson]

Quoting Bloomfield, Jon (2019-07-26 00:21:47)
> > -----Original Message-----
> > From: Chris Wilson <chris at chris-wilson.co.uk>
> > Sent: Thursday, July 25, 2019 4:17 PM
> > To: intel-gfx at lists.freedesktop.org
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>; Joonas Lahtinen
> > <joonas.lahtinen at linux.intel.com>; Ursulin, Tvrtko <tvrtko.ursulin at intel.com>;
> > Bloomfield, Jon <jon.bloomfield at intel.com>
> > Subject: [PATCH] drm/i915: Replace hangcheck by heartbeats
> > 
> > Replace sampling the engine state every so often with a periodic
> > heartbeat request to measure the health of an engine. This is coupled
> > with the forced-preemption to allow long running requests to survive so
> > long as they do not block other users.
> 
> Can you explain why we would need this at all if we have forced-preemption?
> Forced preemption guarantees that an engine cannot interfere with the timely
> execution of other contexts. If it hangs, but nothing else wants to use the engine
> then do we care?

We may not have something else waiting to use the engine, but we may
have users waiting for the response where we need to detect the GPU hang
to prevent an infinite wait / stuck processes and infinite power drain.

There is also the secondary task of flushing idle barriers.

> Power, obviously. But I'm not everything can be pre-empted. If a compute
> context is running on an engine, and no other contexts require that engine,
> then is it  right to nuke it just because it's busy in a long running thread?

Yes. Unless you ask that we implement GPU-isolation where not even the
kernel is allowed to use a particular set of engines.
-Chris