Chris Wilson <ch...@chris-wilson.co.uk> writes: > In the unlikely case (thank you CI!), we may find ourselves wanting to > issue a preemption but having no runnable requests left. In this case, > we set the semaphore before computing the preemption and so must unset > it before forgetting (or else we leave the machine busywaiting until the > next request comes along and so likely hang). > > Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> > --- > drivers/gpu/drm/i915/gt/intel_lrc.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c > b/drivers/gpu/drm/i915/gt/intel_lrc.c > index c8a0c9b32764..efccc31887de 100644 > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c > @@ -233,13 +233,18 @@ static inline u32 intel_hws_preempt_address(struct > intel_engine_cs *engine) > static inline void > ring_set_paused(const struct intel_engine_cs *engine, int state) > { > + u32 *sema = &engine->status_page.addr[I915_GEM_HWS_PREEMPT]; > + > + if (*sema == state) > + return; > +
So you want to avoid useless wmb, as I don't see other benefit. Makes this look suspiciously racy but seems to be just my usual paranoia. > /* > * We inspect HWS_PREEMPT with a semaphore inside > * engine->emit_fini_breadcrumb. If the dword is true, > * the ring is paused as the semaphore will busywait > * until the dword is false. > */ > - engine->status_page.addr[I915_GEM_HWS_PREEMPT] = state; > + *sema = state; > wmb(); > } > > @@ -1243,6 +1248,8 @@ static void execlists_dequeue(struct intel_engine_cs > *engine) > *port = execlists_schedule_in(last, port - execlists->pending); > memset(port + 1, 0, (last_port - port) * sizeof(*port)); > execlists_submit_ports(engine); > + } else { > + ring_set_paused(engine, 0); This looks like a right thing to do. But why did we end up figuring things out wrong in need_preempt()? One would think that if there were nothing to preempt into, we would never set the pause in the first place. Also the preempt to idle cycle mention in effective_prio() seems to be off. Could be that someone forgot to point that out when he did review preempt-to-busy. -Mika > } > } > > -- > 2.20.1 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/intel-gfx _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx