[PATCH v2] drm/i915: Filter out spurious execlists context-switch interrupts

Chris Wilson
2017-10-20T11:48:54Z

Back in commit a4b2b01523a8 ("drm/i915: Don't mark an execlists
context-switch when idle") we noticed the presence of late
context-switch interrupts. We were able to filter those out by looking
at whether the ELSP remained active, but in commit beecec901790
("drm/i915/execlists: Preemption!") that became problematic as we now
anticipate receiving a context-switch event for preemption while ELSP
may be empty. To restore the spurious interrupt suppression, add a
counter for the expected number of pending context-switches and skip if
we do not need to handle this interrupt to make forward progress.

v2: Add the missing inc(active) for preempt.

Fixes: beecec901790 ("drm/i915/execlists: Preemption!")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michal Winiarski <michal.winiarski@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
---
drivers/gpu/drm/i915/i915_guc_submission.c | 11 ++++++-----
drivers/gpu/drm/i915/i915_irq.c | 6 ++++--
drivers/gpu/drm/i915/intel_engine_cs.c | 5 +++--
drivers/gpu/drm/i915/intel_lrc.c | 22 ++++++++++++++++++----
drivers/gpu/drm/i915/intel_ringbuffer.h | 7 +++++++
5 files changed, 38 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index a2e8114b739d..c22d0a07467c 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -550,11 +550,9 @@ static void port_assign(struct execlist_port *port,
struct drm_i915_gem_request *rq)
{
GEM_BUG_ON(rq == port_request(port));
+ GEM_BUG_ON(port_isset(port));

- if (port_isset(port))
- i915_gem_request_put(port_request(port));
-
- port_set(port, port_pack(i915_gem_request_get(rq), port_count(port)));
+ port_set(port, i915_gem_request_get(rq));
nested_enable_signaling(rq);
}

@@ -586,8 +584,10 @@ static void i915_guc_dequeue(struct intel_engine_cs *engine)
goto done;
}

- if (submit)
+ if (submit) {
port_assign(port, last);
+ execlists->active++;
+ }
port++;
}

@@ -610,6 +610,7 @@ static void i915_guc_dequeue(struct intel_engine_cs *engine)
execlists->first = rb;
if (submit) {
port_assign(port, last);
+ execlists->active++;
i915_guc_submit(engine);
}
spin_unlock_irq(&engine->timeline->lock);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index b1296a55c1e4..f8205841868b 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1388,8 +1388,10 @@ gen8_cs_irq_handler(struct intel_engine_cs *engine, u32 iir, int test_shift)
bool tasklet = false;

if (iir & (GT_CONTEXT_SWITCH_INTERRUPT << test_shift)) {
- __set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
- tasklet = true;
+ if (READ_ONCE(engine->execlists.active)) {
+ __set_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
+ tasklet = true;
+ }
}

if (iir & (GT_RENDER_USER_INTERRUPT << test_shift)) {
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index a47a9c6bea52..8aecbc321786 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1548,8 +1548,8 @@ bool intel_engine_is_idle(struct intel_engine_cs *engine)
if (test_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted))
return false;

- /* Both ports drained, no more ELSP submission? */
- if (port_request(&engine->execlists.port[0]))
+ /* Waiting to drain ELSP? */
+ if (READ_ONCE(engine->execlists.active))
return false;

/* ELSP is empty, but there are ready requests? */
@@ -1749,6 +1749,7 @@ void intel_engine_dump(struct intel_engine_cs *engine, struct drm_printer *m)
idx);
}
}
+ drm_printf(m, "\t\tELSP active %d\n", execlists->active);
rcu_read_unlock();
} else if (INTEL_GEN(dev_priv) > 6) {
drm_printf(m, "\tPP_DIR_BASE: 0x%08x\n",
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 7f45dd7dc3e5..c2cdb85db365 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -482,15 +482,23 @@ static bool can_merge_ctx(const struct i915_gem_context *prev,
return true;
}

-static void port_assign(struct execlist_port *port,
+static bool port_assign(struct execlist_port *port,
struct drm_i915_gem_request *rq)
{
+ bool was_idle;
+
GEM_BUG_ON(rq == port_request(port));

- if (port_isset(port))
+ if (port_isset(port)) {
i915_gem_request_put(port_request(port));
+ was_idle = false;
+ } else {
+ was_idle = true;
+ }

port_set(port, port_pack(i915_gem_request_get(rq), port_count(port)));
+
+ return was_idle;
}

static void inject_preempt_context(struct intel_engine_cs *engine)
@@ -576,6 +584,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
*/
inject_preempt_context(engine);
execlists->preempt = true;
+ execlists->active++;
goto unlock;
} else {
/*
@@ -657,7 +666,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
GEM_BUG_ON(last->ctx == rq->ctx);

if (submit)
- port_assign(port, last);
+ execlists->active += port_assign(port, last);
port++;

GEM_BUG_ON(port_isset(port));
@@ -679,7 +688,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
done:
execlists->first = rb;
if (submit)
- port_assign(port, last);
+ execlists->active += port_assign(port, last);
unlock:
spin_unlock_irq(&engine->timeline->lock);

@@ -696,10 +705,12 @@ execlist_cancel_port_requests(struct intel_engine_execlists *execlists)
while (num_ports-- && port_isset(port)) {
struct drm_i915_gem_request *rq = port_request(port);

+ GEM_BUG_ON(!execlists->active);
execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_PREEMPTED);
i915_gem_request_put(rq);

memset(port, 0, sizeof(*port));
+ execlists->active--;
port++;
}
}
@@ -863,6 +874,8 @@ static void intel_lrc_irq_handler(unsigned long data)

GEM_BUG_ON(!execlists->preempt);
execlists->preempt = false;
+ execlists->active--;
+ GEM_BUG_ON(execlists->active);
continue;
}

@@ -1461,6 +1474,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *engine)
clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
execlists->csb_head = -1;
execlists->preempt = false;
+ execlists->active = 0;

/* After a GPU reset, we may have requests to replay */
if (!i915_modparams.enable_guc_submission && execlists->first)
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 17186f067408..588f5fe9d2b7 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -245,6 +245,11 @@ struct intel_engine_execlists {
*/
bool preempt;

+ /**
+ * @active: count of the number of outstanding CSB events
+ */
+ unsigned int active;
+
/**
* @port_mask: number of execlist ports - 1
*/
@@ -538,9 +543,11 @@ execlists_port_complete(struct intel_engine_execlists * const execlists,
const unsigned int m = execlists->port_mask;

GEM_BUG_ON(port_index(port, execlists) != 0);
+ GEM_BUG_ON(!execlists->active);

memmove(port, port + 1, m * sizeof(struct execlist_port));
memset(port + m, 0, sizeof(struct execlist_port));
+ execlists->active--;
}

static inline unsigned int
--
2.15.0.rc1