Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> Currently the timer is armed for 1ms after the first use and is killed
> immediately, dropping the forcewake as early as possible. However, for
> very frequent operations the forcewake dance has a large impact on
> latency and keeping the timer alive until we are idle is preferred. To
> achieve this, if we call intel_uncore_forcewake_get whilst the timer is
> alive (repeated use), then set a flag to restart the timer on expiry
> rather than drop the forcewake usage count. The timer is racy, the
> consequence of the race is to expire the timer earlier than is now
> desired but does not impact on correct behaviour. The offset the race
> slightly, we set the active flag again on intel_uncore_forcewake_put.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_uncore.c | 15 ++++++++++++---
> drivers/gpu/drm/i915/intel_uncore.h | 1 +
> 2 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 7eaa592aed26..2fd0989805eb 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -216,6 +216,9 @@ intel_uncore_fw_release_timer(struct hrtimer *timer)
>
> assert_rpm_device_not_suspended(dev_priv);
>
> + if (xchg(&domain->active, false))
> + return HRTIMER_RESTART;
> +
> spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
> if (WARN_ON(domain->wake_count == 0))
> domain->wake_count++;
> @@ -246,6 +249,7 @@ static void intel_uncore_forcewake_reset(struct drm_i915_private *dev_priv,
> active_domains = 0;
>
> for_each_fw_domain(domain, dev_priv, tmp) {
> + smp_store_mb(domain->active, false);
> if (hrtimer_cancel(&domain->timer) == 0)
> continue;
>
> @@ -453,9 +457,12 @@ static void __intel_uncore_forcewake_get(struct drm_i915_private *dev_priv,
>
> fw_domains &= dev_priv->uncore.fw_domains;
>
> - for_each_fw_domain_masked(domain, fw_domains, dev_priv, tmp)
> - if (domain->wake_count++)
> + for_each_fw_domain_masked(domain, fw_domains, dev_priv, tmp) {
> + if (domain->wake_count++) {
> fw_domains &= ~domain->mask;
> + domain->active = true;
> + }
> + }
>
> if (fw_domains)
> dev_priv->uncore.funcs.force_wake_get(dev_priv, fw_domains);
> @@ -520,8 +527,10 @@ static void __intel_uncore_forcewake_put(struct drm_i915_private *dev_priv,
> if (WARN_ON(domain->wake_count == 0))
> continue;
>
> - if (--domain->wake_count)
> + if (--domain->wake_count) {
> + domain->active = true;
We dont wan't to set the active here for all domains that
are going to power off, and delay their release for one timer tick
to optimistically wait for next user?
-Mika
> continue;
> + }
>
> fw_domain_arm_timer(domain);
> }
> diff --git a/drivers/gpu/drm/i915/intel_uncore.h b/drivers/gpu/drm/i915/intel_uncore.h
> index 5fec5fd4346c..dfead585835c 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.h
> +++ b/drivers/gpu/drm/i915/intel_uncore.h
> @@ -95,6 +95,7 @@ struct intel_uncore {
> struct intel_uncore_forcewake_domain {
> unsigned int mask;
> unsigned int wake_count;
> + bool active;
> struct hrtimer timer;
> i915_reg_t reg_set;
> i915_reg_t reg_ack;
> --
> 2.11.0
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