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authorChris Wilson <chris@chris-wilson.co.uk>2017-12-09 12:47:10 +0000
committerChris Wilson <chris@chris-wilson.co.uk>2017-12-11 17:23:02 +0000
commitb92326a04071ed5a02bc31c2359da2cdadde743c (patch)
tree3b11326102b3c5cd03ea95892cddce74350abe52 /drivers/gpu/drm/i915
parent776bc27fd8ab67a675cb0041d3af361af5d0e290 (diff)
drm/i915: Only report a wakeup if the waiter was truly asleep
If we attempt to wake up a waiter, who is currently checking the seqno it will be in the TASK_INTERRUPTIBLE state and ttwu will report success. However, it is actually awake and functioning -- so delay reporting the actual wake up until it sleeps. This fixes some spurious claims of missed_breadcrumbs when running under heavy load; i.e. sufficient load to preempt away the newly woken waiter before they complete their checks. However, it does so at the cost of a rare false negative; where the waiter changes between the check and ttwu -- the only way to fix that would be to extend the reporting from ttwu where the check could be done atomically. v2: Defend against !CONFIG_SMP v3: Don't filter out calls to wake_up_process v4: Drop risky microoptimisation to skip wakeups Testcase: igt/drv_missed_irq # sanity check we do detect missed_breadcrumb() Testcase: igt/gem_concurrent_blit # for generating false positives References: https://bugs.freedesktop.org/show_bug.cgi?id=100007 Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20171209124710.1606-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Diffstat (limited to 'drivers/gpu/drm/i915')
-rw-r--r--drivers/gpu/drm/i915/intel_breadcrumbs.c26
1 files changed, 22 insertions, 4 deletions
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index a7740696114d..58c624f982d9 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -27,6 +27,12 @@
#include "i915_drv.h"
+#ifdef CONFIG_SMP
+#define task_asleep(tsk) ((tsk)->state & TASK_NORMAL && !(tsk)->on_cpu)
+#else
+#define task_asleep(tsk) ((tsk)->state & TASK_NORMAL)
+#endif
+
static unsigned int __intel_breadcrumbs_wakeup(struct intel_breadcrumbs *b)
{
struct intel_wait *wait;
@@ -36,8 +42,20 @@ static unsigned int __intel_breadcrumbs_wakeup(struct intel_breadcrumbs *b)
wait = b->irq_wait;
if (wait) {
+ /*
+ * N.B. Since task_asleep() and ttwu are not atomic, the
+ * waiter may actually go to sleep after the check, causing
+ * us to suppress a valid wakeup. We prefer to reduce the
+ * number of false positive missed_breadcrumb() warnings
+ * at the expense of a few false negatives, as it it easy
+ * to trigger a false positive under heavy load. Enough
+ * signal should remain from genuine missed_breadcrumb()
+ * for us to detect in CI.
+ */
+ bool was_asleep = task_asleep(wait->tsk);
+
result = ENGINE_WAKEUP_WAITER;
- if (wake_up_process(wait->tsk))
+ if (wake_up_process(wait->tsk) && was_asleep)
result |= ENGINE_WAKEUP_ASLEEP;
}
@@ -77,8 +95,8 @@ static noinline void missed_breadcrumb(struct intel_engine_cs *engine)
static void intel_breadcrumbs_hangcheck(struct timer_list *t)
{
- struct intel_engine_cs *engine = from_timer(engine, t,
- breadcrumbs.hangcheck);
+ struct intel_engine_cs *engine =
+ from_timer(engine, t, breadcrumbs.hangcheck);
struct intel_breadcrumbs *b = &engine->breadcrumbs;
if (!b->irq_armed)
@@ -104,7 +122,7 @@ static void intel_breadcrumbs_hangcheck(struct timer_list *t)
*/
if (intel_engine_wakeup(engine) & ENGINE_WAKEUP_ASLEEP) {
missed_breadcrumb(engine);
- mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
+ mod_timer(&b->fake_irq, jiffies + 1);
} else {
mod_timer(&b->hangcheck, wait_timeout());
}