Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> 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 the only
> writer to execlists->port[] from running at the same time as the enable.
>
> Fixes: 4900727d35bb ("drm/i915/pmu: Reconstruct active state on starting busy-stats")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
This series applied on drm-tip with j1900. Uptime 2h 35min until system
hang. Load was glxgears + video.
-Mika
> ---
> drivers/gpu/drm/i915/intel_engine_cs.c | 20 ++++++++++++--------
> 1 file changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index d790bdc227ff..b221610f2365 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -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)
> --
> 2.15.1
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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