Re: [Intel-gfx] [PATCH] dma-fence: Use non-atomic bitops while under the lock

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

On 03/10/2019 11:12, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> We do not have to use atomic bitops when already under the spinlock.
> 
> Saves on a handful of lock instruction prefixes, on x86 at least.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: dri-devel@lists.freedesktop.org
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/dma-buf/dma-fence.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 2c136aee3e79..f0b480042e2f 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -133,15 +133,15 @@ int dma_fence_signal_locked(struct dma_fence *fence)
>   
>   	lockdep_assert_held(fence->lock);
>   
> -	if (unlikely(test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
> -				      &fence->flags)))
> +	if (unlikely(__test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
> +					&fence->flags)))

This breaks left right and center so I guess it is more subtle than this!

Regards,

Tvrtko

>   		return -EINVAL;
>   
>   	/* Stash the cb_list before replacing it with the timestamp */
>   	list_replace(&fence->cb_list, &cb_list);
>   
>   	fence->timestamp = ktime_get();
> -	set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
> +	__set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
>   	trace_dma_fence_signaled(fence);
>   
>   	list_for_each_entry_safe(cur, tmp, &cb_list, node) {
> @@ -343,8 +343,8 @@ int dma_fence_add_callback(struct dma_fence *fence, struct dma_fence_cb *cb,
>   
>   	spin_lock_irqsave(fence->lock, flags);
>   
> -	was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
> -				   &fence->flags);
> +	was_set = __test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
> +				     &fence->flags);
>   
>   	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
>   		ret = -ENOENT;
> @@ -473,8 +473,8 @@ dma_fence_default_wait(struct dma_fence *fence, bool intr, signed long timeout)
>   		goto out;
>   	}
>   
> -	was_set = test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
> -				   &fence->flags);
> +	was_set = __test_and_set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
> +				     &fence->flags);
>   
>   	if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
>   		goto out;
> 
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