Re: [Intel-gfx] [PATCH 05/66] drm/i915: Skip taking acquire mutex for no ref->active callback

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 15/07/2020 12:50, Chris Wilson wrote:
> If no active callback is defined for i915_active, we do not need to
> serialise its enabling with the mutex. We still do only want to call the
> debug activate once, and must still serialise with a concurrent retire.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_active.c | 25 ++++++++++++++++---------
>   1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
> index d960d0be5bd2..841b5c30950a 100644
> --- a/drivers/gpu/drm/i915/i915_active.c
> +++ b/drivers/gpu/drm/i915/i915_active.c
> @@ -416,6 +416,14 @@ bool i915_active_acquire_if_busy(struct i915_active *ref)
>   	return atomic_add_unless(&ref->count, 1, 0);
>   }
>   
> +static void __i915_active_activate(struct i915_active *ref)
> +{
> +	spin_lock_irq(&ref->tree_lock); /* __active_retire() */
> +	if (!atomic_fetch_inc(&ref->count))
> +		debug_active_activate(ref);
> +	spin_unlock_irq(&ref->tree_lock);
> +}
> +
>   int i915_active_acquire(struct i915_active *ref)
>   {
>   	int err;
> @@ -423,23 +431,22 @@ int i915_active_acquire(struct i915_active *ref)
>   	if (i915_active_acquire_if_busy(ref))
>   		return 0;
>   
> +	if (!ref->active) {
> +		__i915_active_activate(ref);
> +		return 0;
> +	}
> +
>   	err = mutex_lock_interruptible(&ref->mutex);
>   	if (err)
>   		return err;
>   
>   	if (likely(!i915_active_acquire_if_busy(ref))) {
> -		if (ref->active)
> -			err = ref->active(ref);
> -		if (!err) {
> -			spin_lock_irq(&ref->tree_lock); /* __active_retire() */
> -			debug_active_activate(ref);
> -			atomic_inc(&ref->count);
> -			spin_unlock_irq(&ref->tree_lock);
> -		}
> +		err = ref->active(ref);
> +		if (!err)
> +			__i915_active_activate(ref);
>   	}
>   
>   	mutex_unlock(&ref->mutex);
> -

Blank line was nice there.

>   	return err;
>   }
>   
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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