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Commit 99e48bf9 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915: Lock out execlist tasklet while peeking inside for busy-stats 



In order to prevent a race condition where we may end up overaccounting
the active state and leaving the busy-stats believing the GPU is 100%
busy, lock out the tasklet while we reconstruct the busy state. There is
no direct spinlock guard for the execlists->port[], so we need to
utilise tasklet_disable() as a synchronous barrier to prevent it, the
only writer to execlists->port[], from running at the same time as the
enable.

Fixes: 4900727d ("drm/i915/pmu: Reconstruct active state on starting busy-stats")
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180115092041.13509-1-chris@chris-wilson.co.uk


Reviewed-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
parent f255c1e9

drivers/gpu/drm/i915/intel_engine_cs.c

+12 −8
Original line number Diff line number Diff line
@@ -1943,16 +1943,22 @@ intel_engine_lookup_user(struct drm_i915_private *i915, u8 class, u8 instance) 
 */

int intel_enable_engine_stats(struct intel_engine_cs *engine)

{

	struct intel_engine_execlists *execlists = &engine->execlists;

	unsigned long flags;

	int err = 0;



	if (!intel_engine_supports_stats(engine))

		return -ENODEV;



	tasklet_disable(&execlists->tasklet);

	spin_lock_irqsave(&engine->stats.lock, flags);

	if (engine->stats.enabled == ~0)

		goto busy;



	if (unlikely(engine->stats.enabled == ~0)) {

		err = -EBUSY;

		goto unlock;

	}



	if (engine->stats.enabled++ == 0) {

		struct intel_engine_execlists *execlists = &engine->execlists;

		const struct execlist_port *port = execlists->port;

		unsigned int num_ports = execlists_num_ports(execlists);
@@ -1967,14 +1973,12 @@ int intel_enable_engine_stats(struct intel_engine_cs *engine) 
		if (engine->stats.active)

			engine->stats.start = engine->stats.enabled_at;

	}

	spin_unlock_irqrestore(&engine->stats.lock, flags);



	return 0;



busy:

unlock:

	spin_unlock_irqrestore(&engine->stats.lock, flags);

	tasklet_enable(&execlists->tasklet);



	return -EBUSY;

	return err;

}



static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine)