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 <ch...@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com>
---
drivers/gpu/drm/i915/gt/intel_lrc.c | 68 ++++++++++++++---------------
1 file changed, 34 insertions(+), 34 deletions(-)
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c
b/drivers/gpu/drm/i915/gt/intel_lrc.c
index b12355048501..132816235d8a 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 +2186,30 @@ 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);
-
- /*
- * 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);
+ *port = execlists_schedule_in(last, port - execlists->pending);
+ execlists->switch_priority_hint =
+ switch_prio(engine, *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);
+ return true;
}
static void
@@ -2478,7 +2469,16 @@ 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();
}
}
--
2.20.1
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx
