Re: [PATCH v2 1/5] dma-fence: Add deadline awareness

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 07.08.21 um 20:37 schrieb Rob Clark:
> From: Rob Clark <robdclark@chromium.org>
>
> Add a way to hint to the fence signaler of an upcoming deadline, such as
> vblank, which the fence waiter would prefer not to miss.  This is to aid
> the fence signaler in making power management decisions, like boosting
> frequency as the deadline approaches and awareness of missing deadlines
> so that can be factored in to the frequency scaling.
>
> v2: Drop dma_fence::deadline and related logic to filter duplicate
>      deadlines, to avoid increasing dma_fence size.  The fence-context
>      implementation will need similar logic to track deadlines of all
>      the fences on the same timeline.  [ckoenig]
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/dma-buf/dma-fence.c | 20 ++++++++++++++++++++
>   include/linux/dma-fence.h   | 16 ++++++++++++++++
>   2 files changed, 36 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index ce0f5eff575d..1f444863b94d 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -910,6 +910,26 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, uint32_t count,
>   }
>   EXPORT_SYMBOL(dma_fence_wait_any_timeout);
>   
> +
> +/**
> + * dma_fence_set_deadline - set desired fence-wait deadline
> + * @fence:    the fence that is to be waited on
> + * @deadline: the time by which the waiter hopes for the fence to be
> + *            signaled
> + *
> + * Inform the fence signaler of an upcoming deadline, such as vblank, by
> + * which point the waiter would prefer the fence to be signaled by.  This
> + * is intended to give feedback to the fence signaler to aid in power
> + * management decisions, such as boosting GPU frequency if a periodic
> + * vblank deadline is approaching.
> + */
> +void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline)
> +{
> +	if (fence->ops->set_deadline && !dma_fence_is_signaled(fence))
> +		fence->ops->set_deadline(fence, deadline);
> +}
> +EXPORT_SYMBOL(dma_fence_set_deadline);
> +
>   /**
>    * dma_fence_init - Initialize a custom fence.
>    * @fence: the fence to initialize
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 6ffb4b2c6371..9c809f0d5d0a 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -99,6 +99,7 @@ enum dma_fence_flag_bits {
>   	DMA_FENCE_FLAG_SIGNALED_BIT,
>   	DMA_FENCE_FLAG_TIMESTAMP_BIT,
>   	DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
> +	DMA_FENCE_FLAG_HAS_DEADLINE_BIT,
>   	DMA_FENCE_FLAG_USER_BITS, /* must always be last member */
>   };
>   
> @@ -261,6 +262,19 @@ struct dma_fence_ops {
>   	 */
>   	void (*timeline_value_str)(struct dma_fence *fence,
>   				   char *str, int size);
> +
> +	/**
> +	 * @set_deadline:
> +	 *
> +	 * Callback to allow a fence waiter to inform the fence signaler of an
> +	 * upcoming deadline, such as vblank, by which point the waiter would
> +	 * prefer the fence to be signaled by.  This is intended to give feedback
> +	 * to the fence signaler to aid in power management decisions, such as
> +	 * boosting GPU frequency.
> +	 *
> +	 * This callback is optional.
> +	 */
> +	void (*set_deadline)(struct dma_fence *fence, ktime_t deadline);
>   };
>   
>   void dma_fence_init(struct dma_fence *fence, const struct dma_fence_ops *ops,
> @@ -586,6 +600,8 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
>   	return ret < 0 ? ret : 0;
>   }
>   
> +void dma_fence_set_deadline(struct dma_fence *fence, ktime_t deadline);
> +
>   struct dma_fence *dma_fence_get_stub(void);
>   struct dma_fence *dma_fence_allocate_private_stub(void);
>   u64 dma_fence_context_alloc(unsigned num);