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

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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: 4900727d35 ("drm/i915/pmu: Reconstruct active state on starting busy-stats")
Signed-off-by: Chris 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: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
(cherry picked from commit 99e48bf98d)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180213095747.2424-1-tvrtko.ursulin@linux.intel.com
This commit is contained in:
Chris Wilson 2018-02-13 09:57:44 +00:00 committed by Rodrigo Vivi
parent 117172c8f9
commit edb76b01ac
1 changed files with 13 additions and 9 deletions
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22
drivers/gpu/drm/i915/intel_engine_cs.c
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@ -1945,16 +1945,22 @@ 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);
@ -1969,14 +1975,12 @@ int intel_enable_engine_stats(struct intel_engine_cs *engine)
if (engine->stats.active)
engine->stats.start = engine->stats.enabled_at;
}
unlock:
spin_unlock_irqrestore(&engine->stats.lock, flags);
tasklet_enable(&execlists->tasklet);
return 0;
busy:
spin_unlock_irqrestore(&engine->stats.lock, flags);
return -EBUSY;
return err;
}
static ktime_t __intel_engine_get_busy_time(struct intel_engine_cs *engine)