From a7980a640cbd339aa80f406d1786a275a2c320bc Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 4 Apr 2017 13:05:31 +0100 Subject: [PATCH] drm/i915: Apply a cond_resched() to the saturated signaler 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. v2: Tvrtko dug into cond_resched() on x86 and found that it only depended upon preempt_count and not tif_need_resched() - which means that we would always call schedule() at that point. Fixes: c81d46138da6 ("drm/i915: Convert trace-irq to the breadcrumb waiter") Signed-off-by: Chris Wilson Cc: Mika Kuoppala Cc: Tvrtko Ursulin Link: http://patchwork.freedesktop.org/patch/msgid/20170404120531.10737-1-chris@chris-wilson.co.uk Reviewed-by: Tvrtko Ursulin --- drivers/gpu/drm/i915/intel_breadcrumbs.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c index 308c56a021ab..9ccbf26124c6 100644 --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c @@ -580,6 +580,8 @@ static int intel_breadcrumbs_signaler(void *arg) signaler_set_rtpriority(); do { + bool do_schedule = true; + set_current_state(TASK_INTERRUPTIBLE); /* We are either woken up by the interrupt bottom-half, @@ -626,7 +628,18 @@ static int intel_breadcrumbs_signaler(void *arg) spin_unlock_irq(&b->rb_lock); i915_gem_request_put(request); - } else { + + /* 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 + * and relinquish the CPU if we burn through the + * entire RT timeslice! + */ + do_schedule = need_resched(); + } + + if (unlikely(do_schedule)) { DEFINE_WAIT(exec); if (kthread_should_park()) -- 2.20.1