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drm/i915: Apply a cond_resched() to the saturated signaler

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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: c81d46138d ("drm/i915: Convert trace-irq to the breadcrumb waiter")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170404120531.10737-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
(cherry picked from commit a7980a640c)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
This commit is contained in:
Chris Wilson 2017-04-04 13:05:31 +01:00 committed by Jani Nikula
parent 1676a2b35c
commit d445aaaac0
1 changed files with 14 additions and 1 deletions
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15
drivers/gpu/drm/i915/intel_breadcrumbs.c
View file

@ -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())