[Intel-gfx] [PATCH] drm/i915/gt: Move execlists_reset() out of line

[Chris Wilson]

Quoting Tvrtko Ursulin (2021-01-21 10:55:49)
> 
> On 21/01/2021 00:32, Chris Wilson wrote:
> > Reduce the bulk of execlists_submission_tasklet by moving the unlikely
> > reset function out of line.
> > 
> > add/remove: 1/0 grow/shrink: 0/1 up/down: 960/-935 (25)
> > Function                                     old     new   delta
> > execlists_reset                                -     960    +960
> > execlists_submission_tasklet                6629    5694    -935
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >   .../drm/i915/gt/intel_execlists_submission.c  | 36 +++++++++----------
> >   1 file changed, 17 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> > index 740ff05fd692..43cc85241886 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> > @@ -2299,10 +2299,13 @@ static void execlists_capture(struct intel_engine_cs *engine)
> >       kfree(cap);
> >   }
> >   
> > -static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
> > +static noinline void execlists_reset(struct intel_engine_cs *engine)
> >   {
> > +     struct intel_engine_execlists *el = &engine->execlists;
> >       const unsigned int bit = I915_RESET_ENGINE + engine->id;
> >       unsigned long *lock = &engine->gt->reset.flags;
> > +     unsigned long eir = fetch_and_zero(&el->error_interrupt);
> 
> We got the locking wrong for this one. Irq handler side is under 
> gt->irq_lock, but there are unlocked rmw cycles in the tasklet. Not 
> counting this fetch_and_zero which is also unlocked.

It doesn't require locking.
-Chris