Back in commit 27af5eea54d1 ("drm/i915: Move execlists irq handler to a
bottom half"), we came to the conclusion that running our CSB processing
and ELSP submission from inside the irq handler was a bad idea. A really
bad idea as we could impose nearly 1s latency on other users of the
system, on average! Deferring our work to a tasklet allowed us to do the
processing with irqs enabled, reducing the impact to an average of about
50us.
We have since eradicated the use of forcewaked mmio from inside the CSB
processing and ELSP submission, bringing the impact down to around 5us
(on Kabylake); an order of magnitude better than our measurements 2
years ago on Broadwell and only about 2x worse on average than the
gem_syslatency on an unladen system.
Comparing the impact on the maximum latency observed over a 120s interval,
repeated several times (using gem_syslatency, similar to RT's cyclictest)
while the system is fully laden with i915 nops, we see that direct
submission definitely worsens the response but not to the same outlandish
degree as before.
x Unladen baseline
+ Using tasklet
* Direct submission
+------------------------------------------------------------------------+
|xx x ++ +++ + * * * ** *** * *|
||A| |__AM__| |_____A_M___| |
+------------------------------------------------------------------------+
N Min Max Median Avg Stddev
x 10 5 18 10 9.3 3.6530049
+ 10 72 120 108 102.9 15.758243
* 10 255 348 316 305.7 28.74814
And with a background load
+------------------------------------------------------------------------+
|x + * * |
|x + + + + + + +* * ** ++ * * * *|
|A |_______A_____|__|_______A___M______| |
+------------------------------------------------------------------------+
N Min Max Median Avg Stddev
x 10 4 11 9 8.5 2.1730675
+ 10 633 1388 972 993 243.33744
* 10 1152 2109 1608 1488.3 314.80719
References: 27af5eea54d1 ("drm/i915: Move execlists irq handler to a bottom half")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_irq.c | 11 ++------
drivers/gpu/drm/i915/intel_lrc.c | 44 +++++++++++++++++---------------
2 files changed, 26 insertions(+), 29 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 3f139ff64385..8b61ebf5cb4a 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1462,22 +1462,15 @@ static void snb_gt_irq_handler(struct drm_i915_private *dev_priv,
static void
gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
{
- bool tasklet = false;
-
- if (iir & GT_CONTEXT_SWITCH_INTERRUPT) {
+ if (iir & GT_CONTEXT_SWITCH_INTERRUPT)
intel_engine_handle_execlists_irq(engine);
- tasklet = true;
- }
if (iir & GT_RENDER_USER_INTERRUPT) {
if (intel_engine_uses_guc(engine))
- tasklet = true;
+ tasklet_hi_schedule(&engine->execlists.tasklet);
notify_ring(engine);
}
-
- if (tasklet)
- tasklet_hi_schedule(&engine->execlists.tasklet);
}
static void gen8_gt_irq_ack(struct drm_i915_private *i915,
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 954eb3a71051..37839d89e03a 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -575,7 +575,7 @@ static void complete_preempt_context(struct intel_engine_execlists *execlists)
execlists_clear_active(execlists, EXECLISTS_ACTIVE_PREEMPT);
}
-static void __execlists_dequeue(struct intel_engine_cs *engine)
+static void execlists_dequeue(struct intel_engine_cs *engine)
{
struct intel_engine_execlists * const execlists = &engine->execlists;
struct execlist_port *port = execlists->port;
@@ -587,7 +587,11 @@ static void __execlists_dequeue(struct intel_engine_cs *engine)
lockdep_assert_held(&engine->timeline.lock);
- /* Hardware submission is through 2 ports. Conceptually each port
+ if (execlists_is_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT))
+ return;
+
+ /*
+ * Hardware submission is through 2 ports. Conceptually each port
* has a (RING_START, RING_HEAD, RING_TAIL) tuple. RING_START is
* static for a context, and unique to each, so we only execute
* requests belonging to a single context from each ring. RING_HEAD
@@ -777,15 +781,6 @@ static void __execlists_dequeue(struct intel_engine_cs *engine)
!port_isset(engine->execlists.port));
}
-static void execlists_dequeue(struct intel_engine_cs *engine)
-{
- unsigned long flags;
-
- spin_lock_irqsave(&engine->timeline.lock, flags);
- __execlists_dequeue(engine);
- spin_unlock_irqrestore(&engine->timeline.lock, flags);
-}
-
void
execlists_cancel_port_requests(struct intel_engine_execlists * const execlists)
{
@@ -1106,6 +1101,7 @@ void intel_engine_handle_execlists_irq(struct intel_engine_cs *engine)
execlists->csb_read);
execlists->csb_head = head;
+ execlists_dequeue(engine);
spin_unlock(&engine->timeline.lock);
}
@@ -1122,8 +1118,9 @@ static void execlists_submission_tasklet(unsigned long data)
engine->i915->gt.awake,
engine->execlists.active);
- if (!execlists_is_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT))
- execlists_dequeue(engine);
+ spin_lock_irq(&engine->timeline.lock);
+ execlists_dequeue(engine);
+ spin_unlock_irq(&engine->timeline.lock);
}
static void queue_request(struct intel_engine_cs *engine,
@@ -1134,16 +1131,20 @@ static void queue_request(struct intel_engine_cs *engine,
&lookup_priolist(engine, prio)->requests);
}
-static void __submit_queue(struct intel_engine_cs *engine, int prio)
+static void __update_queue(struct intel_engine_cs *engine, int prio)
{
engine->execlists.queue_priority = prio;
- tasklet_hi_schedule(&engine->execlists.tasklet);
}
static void submit_queue(struct intel_engine_cs *engine, int prio)
{
- if (prio > engine->execlists.queue_priority)
- __submit_queue(engine, prio);
+ if (prio > engine->execlists.queue_priority) {
+ __update_queue(engine, prio);
+ if (!intel_engine_uses_guc(engine))
+ execlists_dequeue(engine);
+ else
+ tasklet_hi_schedule(&engine->execlists.tasklet);
+ }
}
static void execlists_submit_request(struct i915_request *request)
@@ -1155,11 +1156,12 @@ static void execlists_submit_request(struct i915_request *request)
spin_lock_irqsave(&engine->timeline.lock, flags);
queue_request(engine, &request->sched, rq_prio(request));
- submit_queue(engine, rq_prio(request));
GEM_BUG_ON(!engine->execlists.first);
GEM_BUG_ON(list_empty(&request->sched.link));
+ submit_queue(engine, rq_prio(request));
+
spin_unlock_irqrestore(&engine->timeline.lock, flags);
}
@@ -1286,8 +1288,10 @@ static void execlists_schedule(struct i915_request *request,
}
if (prio > engine->execlists.queue_priority &&
- i915_sw_fence_done(&sched_to_request(node)->submit))
- __submit_queue(engine, prio);
+ i915_sw_fence_done(&sched_to_request(node)->submit)) {
+ __update_queue(engine, prio);
+ tasklet_hi_schedule(&engine->execlists.tasklet);
+ }
}
spin_unlock_irq(&engine->timeline.lock);
--
2.17.0
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