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Subject: Re: [RFC 1/3] dma-fence: Add boost fence op
To:     Rob Clark <robdclark@gmail.com>, dri-devel@lists.freedesktop.org
Cc:     freedreno@lists.freedesktop.org, linux-arm-msm@vger.kernel.org,
        Rob Clark <robdclark@chromium.org>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@vger.kernel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@lists.linaro.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20210519183855.1523927-1-robdclark@gmail.com>
 <20210519183855.1523927-2-robdclark@gmail.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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Uff, that looks very hardware specific to me.

As far as I can see you can also implement completely inside the backend 
by starting a timer on enable_signaling, don't you?

Christian.

Am 19.05.21 um 20:38 schrieb Rob Clark:
> From: Rob Clark <robdclark@chromium.org>
>
> Add a way to hint to the fence signaler that a fence waiter has missed a
> deadline waiting on the fence.
>
> In some cases, missing a vblank can result in lower gpu utilization,
> when really we want to go in the opposite direction and boost gpu freq.
> The boost callback gives some feedback to the fence signaler that we
> are missing deadlines, so it can take this into account in it's freq/
> utilization calculations.
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>   include/linux/dma-fence.h | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
>
> diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
> index 9f12efaaa93a..172702521acc 100644
> --- a/include/linux/dma-fence.h
> +++ b/include/linux/dma-fence.h
> @@ -231,6 +231,17 @@ struct dma_fence_ops {
>   	signed long (*wait)(struct dma_fence *fence,
>   			    bool intr, signed long timeout);
>   
> +	/**
> +	 * @boost:
> +	 *
> +	 * Optional callback, to indicate that a fence waiter missed a deadline.
> +	 * This can serve as a signal that (if possible) whatever signals the
> +	 * fence should boost it's clocks.
> +	 *
> +	 * This can be called in any context that can call dma_fence_wait().
> +	 */
> +	void (*boost)(struct dma_fence *fence);
> +
>   	/**
>   	 * @release:
>   	 *
> @@ -586,6 +597,21 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
>   	return ret < 0 ? ret : 0;
>   }
>   
> +/**
> + * dma_fence_boost - hint from waiter that it missed a deadline
> + *
> + * @fence: the fence that caused the missed deadline
> + *
> + * This function gives a hint from a fence waiter that a deadline was
> + * missed, so that the fence signaler can factor this in to device
> + * power state decisions
> + */
> +static inline void dma_fence_boost(struct dma_fence *fence)
> +{
> +	if (fence->ops->boost)
> +		fence->ops->boost(fence);
> +}
> +
>   struct dma_fence *dma_fence_get_stub(void);
>   u64 dma_fence_context_alloc(unsigned num);
>