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    SubjectRe: [PATCH v3 1/9] dma-fence: Add deadline awareness
    On Fri, Sep 03, 2021 at 11:47:52AM -0700, Rob Clark wrote:
    > 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>
    > Signed-off-by: Rob Clark <robdclark@chromium.org>
    > ---
    > 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.

    Please add here that this callback is called without &dma_fence.lock held,
    and that locking is up to callers if they have some state to manage.

    I realized that while scratching some heads over your later patches.
    -Daniel

    > + *
    > + * 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);
    > --
    > 2.31.1
    >

    --
    Daniel Vetter
    Software Engineer, Intel Corporation
    http://blog.ffwll.ch

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