Re: [PATCH 12/19] drm/i915/gt: Declare timeline.lock to be irq-free

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

On 18/11/2019 23:02, Chris Wilson wrote:
> Now that we never allow the intel_wakeref callbacks to be invoked from
> interrupt context, we do not need the irqsafe spinlock for the timeline.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/gt/intel_gt_requests.c |  9 ++++-----
>   drivers/gpu/drm/i915/gt/intel_reset.c       |  9 ++++-----
>   drivers/gpu/drm/i915/gt/intel_timeline.c    | 10 ++++------
>   3 files changed, 12 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> index 7559d6373f49..74356db43325 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
> @@ -33,7 +33,6 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
>   {
>   	struct intel_gt_timelines *timelines = &gt->timelines;
>   	struct intel_timeline *tl, *tn;
> -	unsigned long flags;
>   	bool interruptible;
>   	LIST_HEAD(free);
>   
> @@ -43,7 +42,7 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
>   
>   	flush_submission(gt); /* kick the ksoftirqd tasklets */
>   
> -	spin_lock_irqsave(&timelines->lock, flags);
> +	spin_lock(&timelines->lock);
>   	list_for_each_entry_safe(tl, tn, &timelines->active_list, link) {
>   		if (!mutex_trylock(&tl->mutex))
>   			continue;
> @@ -51,7 +50,7 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
>   		intel_timeline_get(tl);
>   		GEM_BUG_ON(!atomic_read(&tl->active_count));
>   		atomic_inc(&tl->active_count); /* pin the list element */
> -		spin_unlock_irqrestore(&timelines->lock, flags);
> +		spin_unlock(&timelines->lock);
>   
>   		if (timeout > 0) {
>   			struct dma_fence *fence;
> @@ -67,7 +66,7 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
>   
>   		retire_requests(tl);
>   
> -		spin_lock_irqsave(&timelines->lock, flags);
> +		spin_lock(&timelines->lock);
>   
>   		/* Resume iteration after dropping lock */
>   		list_safe_reset_next(tl, tn, link);
> @@ -82,7 +81,7 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
>   			list_add(&tl->link, &free);
>   		}
>   	}
> -	spin_unlock_irqrestore(&timelines->lock, flags);
> +	spin_unlock(&timelines->lock);
>   
>   	list_for_each_entry_safe(tl, tn, &free, link)
>   		__intel_timeline_free(&tl->kref);
> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
> index 0388f9375366..36189238e13c 100644
> --- a/drivers/gpu/drm/i915/gt/intel_reset.c
> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c
> @@ -831,7 +831,6 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
>   {
>   	struct intel_gt_timelines *timelines = &gt->timelines;
>   	struct intel_timeline *tl;
> -	unsigned long flags;
>   	bool ok;
>   
>   	if (!test_bit(I915_WEDGED, &gt->reset.flags))
> @@ -853,7 +852,7 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
>   	 *
>   	 * No more can be submitted until we reset the wedged bit.
>   	 */
> -	spin_lock_irqsave(&timelines->lock, flags);
> +	spin_lock(&timelines->lock);
>   	list_for_each_entry(tl, &timelines->active_list, link) {
>   		struct dma_fence *fence;
>   
> @@ -861,7 +860,7 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
>   		if (!fence)
>   			continue;
>   
> -		spin_unlock_irqrestore(&timelines->lock, flags);
> +		spin_unlock(&timelines->lock);
>   
>   		/*
>   		 * All internal dependencies (i915_requests) will have
> @@ -874,10 +873,10 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
>   		dma_fence_put(fence);
>   
>   		/* Restart iteration after droping lock */
> -		spin_lock_irqsave(&timelines->lock, flags);
> +		spin_lock(&timelines->lock);
>   		tl = list_entry(&timelines->active_list, typeof(*tl), link);
>   	}
> -	spin_unlock_irqrestore(&timelines->lock, flags);
> +	spin_unlock(&timelines->lock);
>   
>   	/* We must reset pending GPU events before restoring our submission */
>   	ok = !HAS_EXECLISTS(gt->i915); /* XXX better agnosticism desired */
> diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.c b/drivers/gpu/drm/i915/gt/intel_timeline.c
> index 4f914f0d5eab..bd973d950064 100644
> --- a/drivers/gpu/drm/i915/gt/intel_timeline.c
> +++ b/drivers/gpu/drm/i915/gt/intel_timeline.c
> @@ -332,7 +332,6 @@ int intel_timeline_pin(struct intel_timeline *tl)
>   void intel_timeline_enter(struct intel_timeline *tl)
>   {
>   	struct intel_gt_timelines *timelines = &tl->gt->timelines;
> -	unsigned long flags;
>   
>   	/*
>   	 * Pretend we are serialised by the timeline->mutex.
> @@ -358,16 +357,15 @@ void intel_timeline_enter(struct intel_timeline *tl)
>   	if (atomic_add_unless(&tl->active_count, 1, 0))
>   		return;
>   
> -	spin_lock_irqsave(&timelines->lock, flags);
> +	spin_lock(&timelines->lock);
>   	if (!atomic_fetch_inc(&tl->active_count))
>   		list_add(&tl->link, &timelines->active_list);
> -	spin_unlock_irqrestore(&timelines->lock, flags);
> +	spin_unlock(&timelines->lock);
>   }
>   
>   void intel_timeline_exit(struct intel_timeline *tl)
>   {
>   	struct intel_gt_timelines *timelines = &tl->gt->timelines;
> -	unsigned long flags;
>   
>   	/* See intel_timeline_enter() */
>   	lockdep_assert_held(&tl->mutex);
> @@ -376,10 +374,10 @@ void intel_timeline_exit(struct intel_timeline *tl)
>   	if (atomic_add_unless(&tl->active_count, -1, 1))
>   		return;
>   
> -	spin_lock_irqsave(&timelines->lock, flags);
> +	spin_lock(&timelines->lock);
>   	if (atomic_dec_and_test(&tl->active_count))
>   		list_del(&tl->link);
> -	spin_unlock_irqrestore(&timelines->lock, flags);
> +	spin_unlock(&timelines->lock);
>   
>   	/*
>   	 * Since this timeline is idle, all bariers upon which we were waiting
> 

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

Regards,

Tvrtko
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