Messages in this thread | | | Subject | Re: [RFC 1/4] dma-fence: Add deadline awareness | From | Christian König <> | Date | Tue, 27 Jul 2021 09:11:44 +0200 |
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Am 27.07.21 um 01:38 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. > > Signed-off-by: Rob Clark <robdclark@chromium.org> > --- > drivers/dma-buf/dma-fence.c | 39 +++++++++++++++++++++++++++++++++++++ > include/linux/dma-fence.h | 17 ++++++++++++++++ > 2 files changed, 56 insertions(+) > > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c > index ce0f5eff575d..2e0d25ab457e 100644 > --- a/drivers/dma-buf/dma-fence.c > +++ b/drivers/dma-buf/dma-fence.c > @@ -910,6 +910,45 @@ 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) > +{ > + unsigned long flags; > + > + if (dma_fence_is_signaled(fence)) > + return; > + > + spin_lock_irqsave(fence->lock, flags); > + > + /* If we already have an earlier deadline, keep it: */ > + if (test_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, &fence->flags) && > + ktime_before(fence->deadline, deadline)) { > + spin_unlock_irqrestore(fence->lock, flags); > + return; > + } > + > + fence->deadline = deadline; > + set_bit(DMA_FENCE_FLAG_HAS_DEADLINE_BIT, &fence->flags); > + > + spin_unlock_irqrestore(fence->lock, flags); > + > + if (fence->ops->set_deadline) > + 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..4e6cfe4e6fbc 100644 > --- a/include/linux/dma-fence.h > +++ b/include/linux/dma-fence.h > @@ -88,6 +88,7 @@ struct dma_fence { > /* @timestamp replaced by @rcu on dma_fence_release() */ > struct rcu_head rcu; > }; > + ktime_t deadline;
Mhm, adding the flag sounds ok to me but I'm a bit hesitating adding the deadline as extra field here.
We tuned the dma_fence structure intentionally so that it is only 64 bytes.
Regards, Christian.
> u64 context; > u64 seqno; > unsigned long flags; > @@ -99,6 +100,7 @@ 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 +263,19 @@ 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 +601,8 @@ 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);
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