Re: [PATCH v9 12/15] drm/msm: Add deadline based boost support

[Dmitry Baryshkov]

On 03/03/2023 01:53, Rob Clark wrote:
> From: Rob Clark <robdclark@xxxxxxxxxxxx>
>
> Track the nearest deadline on a fence timeline and set a timer to expire
> shortly before to trigger boost if the fence has not yet been signaled.
>
> v2: rebase
>
> Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> ---
>   drivers/gpu/drm/msm/msm_fence.c | 74 +++++++++++++++++++++++++++++++++
>   drivers/gpu/drm/msm/msm_fence.h | 20 +++++++++
>   2 files changed, 94 insertions(+)

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>

A small question: do we boost to fit into the deadline or to miss the 
deadline for as little as possible? If the former is the case, we might 
need to adjust 3ms depending on the workload.

> diff --git a/drivers/gpu/drm/msm/msm_fence.c b/drivers/gpu/drm/msm/msm_fence.c
> index 56641408ea74..51b461f32103 100644
> --- a/drivers/gpu/drm/msm/msm_fence.c
> +++ b/drivers/gpu/drm/msm/msm_fence.c
> @@ -8,6 +8,35 @@
>   
>   #include "msm_drv.h"
>   #include "msm_fence.h"
> +#include "msm_gpu.h"
> +
> +static struct msm_gpu *fctx2gpu(struct msm_fence_context *fctx)
> +{
> +	struct msm_drm_private *priv = fctx->dev->dev_private;
> +	return priv->gpu;
> +}
> +
> +static enum hrtimer_restart deadline_timer(struct hrtimer *t)
> +{
> +	struct msm_fence_context *fctx = container_of(t,
> +			struct msm_fence_context, deadline_timer);
> +
> +	kthread_queue_work(fctx2gpu(fctx)->worker, &fctx->deadline_work);
> +
> +	return HRTIMER_NORESTART;
> +}
> +
> +static void deadline_work(struct kthread_work *work)
> +{
> +	struct msm_fence_context *fctx = container_of(work,
> +			struct msm_fence_context, deadline_work);
> +
> +	/* If deadline fence has already passed, nothing to do: */
> +	if (msm_fence_completed(fctx, fctx->next_deadline_fence))
> +		return;
> +
> +	msm_devfreq_boost(fctx2gpu(fctx), 2);
> +}
>   
>   
>   struct msm_fence_context *
> @@ -36,6 +65,13 @@ msm_fence_context_alloc(struct drm_device *dev, volatile uint32_t *fenceptr,
>   	fctx->completed_fence = fctx->last_fence;
>   	*fctx->fenceptr = fctx->last_fence;
>   
> +	hrtimer_init(&fctx->deadline_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
> +	fctx->deadline_timer.function = deadline_timer;
> +
> +	kthread_init_work(&fctx->deadline_work, deadline_work);
> +
> +	fctx->next_deadline = ktime_get();
> +
>   	return fctx;
>   }
>   
> @@ -62,6 +98,8 @@ void msm_update_fence(struct msm_fence_context *fctx, uint32_t fence)
>   	spin_lock_irqsave(&fctx->spinlock, flags);
>   	if (fence_after(fence, fctx->completed_fence))
>   		fctx->completed_fence = fence;
> +	if (msm_fence_completed(fctx, fctx->next_deadline_fence))
> +		hrtimer_cancel(&fctx->deadline_timer);
>   	spin_unlock_irqrestore(&fctx->spinlock, flags);
>   }
>   
> @@ -92,10 +130,46 @@ static bool msm_fence_signaled(struct dma_fence *fence)
>   	return msm_fence_completed(f->fctx, f->base.seqno);
>   }
>   
> +static void msm_fence_set_deadline(struct dma_fence *fence, ktime_t deadline)
> +{
> +	struct msm_fence *f = to_msm_fence(fence);
> +	struct msm_fence_context *fctx = f->fctx;
> +	unsigned long flags;
> +	ktime_t now;
> +
> +	spin_lock_irqsave(&fctx->spinlock, flags);
> +	now = ktime_get();
> +
> +	if (ktime_after(now, fctx->next_deadline) ||
> +			ktime_before(deadline, fctx->next_deadline)) {
> +		fctx->next_deadline = deadline;
> +		fctx->next_deadline_fence =
> +			max(fctx->next_deadline_fence, (uint32_t)fence->seqno);
> +
> +		/*
> +		 * Set timer to trigger boost 3ms before deadline, or
> +		 * if we are already less than 3ms before the deadline
> +		 * schedule boost work immediately.
> +		 */
> +		deadline = ktime_sub(deadline, ms_to_ktime(3));
> +
> +		if (ktime_after(now, deadline)) {
> +			kthread_queue_work(fctx2gpu(fctx)->worker,
> +					&fctx->deadline_work);
> +		} else {
> +			hrtimer_start(&fctx->deadline_timer, deadline,
> +					HRTIMER_MODE_ABS);
> +		}
> +	}
> +
> +	spin_unlock_irqrestore(&fctx->spinlock, flags);
> +}
> +
>   static const struct dma_fence_ops msm_fence_ops = {
>   	.get_driver_name = msm_fence_get_driver_name,
>   	.get_timeline_name = msm_fence_get_timeline_name,
>   	.signaled = msm_fence_signaled,
> +	.set_deadline = msm_fence_set_deadline,
>   };
>   
>   struct dma_fence *
> diff --git a/drivers/gpu/drm/msm/msm_fence.h b/drivers/gpu/drm/msm/msm_fence.h
> index 7f1798c54cd1..cdaebfb94f5c 100644
> --- a/drivers/gpu/drm/msm/msm_fence.h
> +++ b/drivers/gpu/drm/msm/msm_fence.h
> @@ -52,6 +52,26 @@ struct msm_fence_context {
>   	volatile uint32_t *fenceptr;
>   
>   	spinlock_t spinlock;
> +
> +	/*
> +	 * TODO this doesn't really deal with multiple deadlines, like
> +	 * if userspace got multiple frames ahead.. OTOH atomic updates
> +	 * don't queue, so maybe that is ok
> +	 */
> +
> +	/** next_deadline: Time of next deadline */
> +	ktime_t next_deadline;
> +
> +	/**
> +	 * next_deadline_fence:
> +	 *
> +	 * Fence value for next pending deadline.  The deadline timer is
> +	 * canceled when this fence is signaled.
> +	 */
> +	uint32_t next_deadline_fence;
> +
> +	struct hrtimer deadline_timer;
> +	struct kthread_work deadline_work;
>   };
>   
>   struct msm_fence_context * msm_fence_context_alloc(struct drm_device *dev,

--
With best wishes
Dmitry