Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> Quoting Tvrtko Ursulin (2020-03-27 15:59:45)
>>
>> On 27/03/2020 11:26, Chris Wilson wrote:
>> > In what seems remarkably similar to the w/a required to not reload an
>> > idle context with HEAD==TAIL, it appears we must prevent the HW from
>> > switching to an idle context in ELSP[1], while simultaneously trying to
>> > preempt the HW to run another context and a continuation of the idle
>> > context (which is no longer idle).
>> >
>> > process_csb: vecs0: cs-irq head=0, tail=1
>> > process_csb: vecs0: csb[1]: status=0x00000882:0x00000020
>> > trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
>> > trace_ports: vecs0: promote { 8b2:32!, 8c0:30 }
>> > trace_ports: vecs0: submit { 8b8:32, 8c0:32 }
>> > process_csb: vecs0: cs-irq head=1, tail=2
>> > process_csb: vecs0: csb[2]: status=0x00000814:0x00000040
>> > trace_ports: vecs0: completed { 8b2:32!, 8c0:30 }
>> > process_csb: vecs0: cs-irq head=2, tail=5
>> > process_csb: vecs0: csb[3]: status=0x00000812:0x00000020
>> > trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
>> > trace_ports: vecs0: promote { 8b8:32!, 8c0:32 }
>> > process_csb: vecs0: csb[4]: status=0x00000814:0x00000060
>> > trace_ports: vecs0: completed { 8b8:32!, 8c0:32 }
>> > process_csb: vecs0: csb[5]: status=0x00000818:0x00000020
>> > trace_ports: vecs0: completed { 8c0:32, 0:0 }
>> > process_csb: vecs0: ring:{start:0x00021000, head:03f8, tail:03f8, ctl:00000000, mode:00000200}
>> > process_csb: vecs0: rq:{start:00021000, head:03c0, tail:0400, seqno:8c0:32, hwsp:30},
>> > process_csb: vecs0: ctx:{start:00021000, head:03f8, tail:03f8},
>> > process_csb: GEM_BUG_ON("context completed before request")
>> >
>> > Fortunately, we just so happen to have a semaphore in place to prevent
>> > the ring HEAD from proceeding past the end of a request that we can use
>> > to fix the HEAD in position as we reprogram ELSP.
>> >
>> > Closes: https://gitlab.freedesktop.org/drm/intel/issues/1501
>> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
>> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
>> > ---
>> > drivers/gpu/drm/i915/gt/intel_gt_irq.c | 2 +
>> > drivers/gpu/drm/i915/gt/intel_lrc.c | 72 +++++++++++++-------------
>> > 2 files changed, 38 insertions(+), 36 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_irq.c b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
>> > index f0e7fd95165a..be3817d99908 100644
>> > --- a/drivers/gpu/drm/i915/gt/intel_gt_irq.c
>> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
>> > @@ -24,6 +24,8 @@ cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
>> > {
>> > bool tasklet = false;
>> >
>> > + ENGINE_TRACE(engine, "iir: %04x\n", iir);
>> > +
>> > if (unlikely(iir & GT_CS_MASTER_ERROR_INTERRUPT)) {
>> > u32 eir;
>> >
>> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > index b12355048501..53650b452bc9 100644
>> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > @@ -1854,7 +1854,7 @@ static inline void clear_ports(struct i915_request **ports, int count)
>> > memset_p((void **)ports, NULL, count);
>> > }
>> >
>> > -static void execlists_dequeue(struct intel_engine_cs *engine)
>> > +static bool execlists_dequeue(struct intel_engine_cs *engine)
>> > {
>> > struct intel_engine_execlists * const execlists = &engine->execlists;
>> > struct i915_request **port = execlists->pending;
>> > @@ -1928,13 +1928,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> > execlists->queue_priority_hint);
>> > record_preemption(execlists);
>> >
>> > - /*
>> > - * Don't let the RING_HEAD advance past the breadcrumb
>> > - * as we unwind (and until we resubmit) so that we do
>> > - * not accidentally tell it to go backwards.
>> > - */
>> > - ring_set_paused(engine, 1);
>> > -
>> > /*
>> > * Note that we have not stopped the GPU at this point,
>> > * so we are unwinding the incomplete requests as they
>> > @@ -1954,7 +1947,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> > last->sched.attr.priority,
>> > execlists->queue_priority_hint);
>> >
>> > - ring_set_paused(engine, 1);
>> > defer_active(engine);
>> >
>> > /*
>> > @@ -1988,7 +1980,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> > * of timeslices, our queue might be.
>> > */
>> > start_timeslice(engine);
>> > - return;
>> > + return false;
>> > }
>> > }
>> > }
>> > @@ -2021,9 +2013,10 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> > }
>> >
>> > if (last && !can_merge_rq(last, rq)) {
>> > + /* leave this for another sibling */
>> > spin_unlock(&ve->base.active.lock);
>> > start_timeslice(engine);
>> > - return; /* leave this for another sibling */
>> > + return false;
>> > }
>> >
>> > ENGINE_TRACE(engine,
>> > @@ -2193,32 +2186,31 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> > * interrupt for secondary ports).
>> > */
>> > execlists->queue_priority_hint = queue_prio(execlists);
>> > + if (!submit)
>> > + return false;
>> >
>> > - if (submit) {
>> > - *port = execlists_schedule_in(last, port - execlists->pending);
>> > - execlists->switch_priority_hint =
>> > - switch_prio(engine, *execlists->pending);
>> > + *port = execlists_schedule_in(last, port - execlists->pending);
>> > + execlists->switch_priority_hint =
>> > + switch_prio(engine, *execlists->pending);
>> >
>> > - /*
>> > - * Skip if we ended up with exactly the same set of requests,
>> > - * e.g. trying to timeslice a pair of ordered contexts
>> > - */
>> > - if (!memcmp(active, execlists->pending,
>> > - (port - execlists->pending + 1) * sizeof(*port))) {
>> > - do
>> > - execlists_schedule_out(fetch_and_zero(port));
>> > - while (port-- != execlists->pending);
>> > -
>> > - goto skip_submit;
>> > - }
>> > - clear_ports(port + 1, last_port - port);
>> > + /*
>> > + * Skip if we ended up with exactly the same set of requests,
>> > + * e.g. trying to timeslice a pair of ordered contexts
>> > + */
>> > + if (!memcmp(active, execlists->pending,
>> > + (port - execlists->pending + 1) * sizeof(*port))) {
>> > + do
>> > + execlists_schedule_out(fetch_and_zero(port));
>> > + while (port-- != execlists->pending);
>> >
>> > - execlists_submit_ports(engine);
>> > - set_preempt_timeout(engine, *active);
>> > - } else {
>> > -skip_submit:
>> > - ring_set_paused(engine, 0);
>> > + return false;
>> > }
>> > + clear_ports(port + 1, last_port - port);
>> > +
>> > + execlists_submit_ports(engine);
>> > + set_preempt_timeout(engine, *active);
>> > + tasklet_hi_schedule(&execlists->tasklet); /* lost interrupt */
>> > + return true;
>> > }
>> >
>> > static void
>> > @@ -2478,7 +2470,16 @@ static void __execlists_submission_tasklet(struct intel_engine_cs *const engine)
>> > lockdep_assert_held(&engine->active.lock);
>> > if (!READ_ONCE(engine->execlists.pending[0])) {
>> > rcu_read_lock(); /* protect peeking at execlists->active */
>> > - execlists_dequeue(engine);
>> > +
>> > + /*
>> > + * Don't let the RING_HEAD advance past the breadcrumb
>> > + * as we unwind (and until we resubmit) so that we do
>> > + * not accidentally tell it to go backwards.
>> > + */
>> > + ring_set_paused(engine, 1);
>> > + if (!execlists_dequeue(engine))
>> > + ring_set_paused(engine, 0);
>> > +
>> > rcu_read_unlock();
>> > }
>> > }
>> > @@ -2816,8 +2817,7 @@ static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
>> > ring_set_paused(engine, 1); /* Freeze the current request in place */
>> > if (execlists_capture(engine))
>> > intel_engine_reset(engine, msg);
>> > - else
>> > - ring_set_paused(engine, 0);
>> > + ring_set_paused(engine, 0);
>> >
>> > tasklet_enable(&engine->execlists.tasklet);
>> > clear_and_wake_up_bit(bit, lock);
>> >
>>
>> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> The problem appears to be that if we lite-restore into a context inside
> the semaphore, it doesn't yield an arbitration point and we do not raise
> a CSB event.
Trying to make senses of it all...
we do not raise == the hardware does not raise?
So if it is about lite restoring, we can't workaround by always making
sure elsp[1] head != tail?
-Mika
>
> Out of the frying pan and into the fire.
> -Chris
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
_______________________________________________
Intel-gfx mailing list
Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/intel-gfx
