[Intel-gfx] [PATCH v2 11/11] drm/i915: Introduce separate status variable for RC6 and LLC ring frequency setup

[Sagar Arun Kamble]

On 10/6/2017 6:25 PM, Chris Wilson wrote:
> Quoting Sagar Arun Kamble (2017-10-06 13:13:40)
>> Defined new struct intel_rc6 to hold RC6 specific state and
>> intel_ring_pstate to hold ring specific state.
>>
>> v2: s/intel_ring_pstate/intel_llc_pstate and rebase. (Chris)
>>
>> Signed-off-by: Sagar Arun Kamble <sagar.a.kamble at intel.com>
>> Cc: Imre Deak <imre.deak at intel.com>
>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
>> Cc: Radoslaw Szwichtenberg <radoslaw.szwichtenberg at intel.com>
>> ---
>>   drivers/gpu/drm/i915/i915_drv.c |  2 +-
>>   drivers/gpu/drm/i915/i915_drv.h | 10 ++++++++
>>   drivers/gpu/drm/i915/intel_pm.c | 57 +++++++++++++++++++++++++++++++----------
>>   3 files changed, 54 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
>> index 470807c..154f231 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.c
>> +++ b/drivers/gpu/drm/i915/i915_drv.c
>> @@ -2502,7 +2502,7 @@ static int intel_runtime_suspend(struct device *kdev)
>>          struct drm_i915_private *dev_priv = to_i915(dev);
>>          int ret;
>>   
>> -       if (WARN_ON_ONCE(!(dev_priv->pm.rps.enabled && intel_rc6_enabled())))
>> +       if (WARN_ON_ONCE(!(dev_priv->pm.rc6.enabled && intel_rc6_enabled())))
>>                  return -ENODEV;
>>   
>>          if (WARN_ON_ONCE(!HAS_RUNTIME_PM(dev_priv)))
>> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>> index 45944a8..a07aa71 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.h
>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>> @@ -1363,8 +1363,18 @@ struct intel_rps {
>>          struct intel_rps_ei ei;
>>   };
>>   
>> +struct intel_rc6 {
>> +       bool enabled;
>> +};
>> +
>> +struct intel_llc_pstate {
>> +       bool configured;
>> +};
>> +
>>   struct intel_gen6_power_mgmt {
>>          struct intel_rps rps;
>> +       struct intel_rc6 rc6;
>> +       struct intel_llc_pstate llc_pstate;
>>          struct delayed_work autoenable_work;
>>   
>>          /*
>> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
>> index 03264fe..df36a6f 100644
>> --- a/drivers/gpu/drm/i915/intel_pm.c
>> +++ b/drivers/gpu/drm/i915/intel_pm.c
>> @@ -7873,7 +7873,12 @@ static void intel_init_emon(struct drm_i915_private *dev_priv)
>>   
>>   static inline void intel_update_ring_freq(struct drm_i915_private *i915)
>>   {
>> +       if (READ_ONCE(i915->pm.llc_pstate.configured))
>> +               return;
> Tell me about how you expect the locking around this function to be.
>
> The READ_ONCE() implies that we are doing a optimistic peek outside of a
> lock, but then we set configured without acquiring a lock, so I assume
> we are inside some lock.
>
> That looks true for all, we don't need READ_ONCE() anymore as we only
> inspect inside the mutex (and so READ_ONCE is giving the wrong
> impression).
>
>> +
>>          gen6_update_ring_freq(i915);
>> +
>> +       i915->pm.llc_pstate.configured = true;
>>   }
>>   
>>   void intel_disable_gt_powersave(struct drm_i915_private *dev_priv)
>>   {
>> -       if (!READ_ONCE(dev_priv->pm.rps.enabled))
>> -               return;
>> -
>>          mutex_lock(&dev_priv->pm.pcu_lock);
>>   
>>          intel_disable_rc6(dev_priv);
>>          intel_disable_rps(dev_priv);
>> +       if (HAS_LLC(dev_priv))
>> +               dev_priv->pm.llc_pstate.configured = false;
> Always clear it? If no llc, it can never be configured.
> Hmm, better if we just made it symmetrical with
> s/intel_update_ring_freq/intel_enable_llc_pstate/ and
> intel_disable_llc_pstate here.
Will update.
>
>>   
>> -       dev_priv->pm.rps.enabled = false;
>>          mutex_unlock(&dev_priv->pm.pcu_lock);
>>   }
>> @@ -8080,7 +8103,10 @@ static void __intel_autoenable_gt_powersave(struct work_struct *work)
>>          struct intel_engine_cs *rcs;
>>          struct drm_i915_gem_request *req;
>>   
>> -       if (READ_ONCE(dev_priv->pm.rps.enabled))
>> +       if (READ_ONCE(dev_priv->pm.rps.enabled) &&
>> +           READ_ONCE(dev_priv->pm.rc6.enabled) &&
>> +           !(HAS_LLC(dev_priv) ^
>> +             READ_ONCE(dev_priv->pm.llc_pstate.configured)))
>>                  goto out;
> This optimisation has lost its appeal :)
>
> Kill it, if we need something like it we can try again later.
> -Chris
Sure. Understood that using READ_ONCE inside lock was unnecessary.
Will remove this triple condition.