If the engine is continually completing nops, we can saturate the
signaler and keep it working indefinitely. This angers the NMI watchdog!
A good example is to disable semaphores on snb and run igt/gem_exec_nop -
the parallel, multi-engine workloads are more than sufficient to hog the
CPU, preventing the system from even processing ICMP echo replies.
Fixes: c81d46138da6 ("drm/i915: Convert trace-irq to the breadcrumb waiter")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_breadcrumbs.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 1b14c3be6046..763ed497961f 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -622,6 +622,13 @@ static int intel_breadcrumbs_signaler(void *arg)
spin_unlock_irq(&b->rb_lock);
i915_gem_request_put(request);
+
+ /* If the engine is saturated we may be continually
+ * processing completed requests. This angers the
+ * NMI watchdog if we never let anything else
+ * have access to the CPU. Let's pretend to be nice.
+ */
+ cond_resched();
} else {
DEFINE_WAIT(exec);
--
2.11.0
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