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Wed, 28 Jul 2021 07:03:36 +0000 Subject: Re: [RFC 1/4] dma-fence: Add deadline awareness To: Rob Clark , =?UTF-8?Q?Christian_K=c3=b6nig?= Cc: dri-devel , Daniel Vetter , Matthew Brost , Rob Clark , Sumit Semwal , Gustavo Padovan , "open list:SYNC FILE FRAMEWORK" , "moderated list:DMA BUFFER SHARING FRAMEWORK" , open list References: <20210726233854.2453899-1-robdclark@gmail.com> <20210726233854.2453899-2-robdclark@gmail.com> <50b181fe-6605-b7ac-36a6-8bcda2930e6f@gmail.com> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <9edd7083-e6b3-b230-c273-8f2fbe76ca17@amd.com> Date: Wed, 28 Jul 2021 09:03:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-ClientProxiedBy: FR3P281CA0037.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:4a::21) To MN2PR12MB3775.namprd12.prod.outlook.com (2603:10b6:208:159::19) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2a02:908:1252:fb60:502c:190e:1ca:e49a] (2a02:908:1252:fb60:502c:190e:1ca:e49a) by FR3P281CA0037.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:4a::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4373.11 via Frontend Transport; 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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 >>> --- >>> 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. > Hmm, then I guess you wouldn't be a fan of also adding an hrtimer? > > We could push the ktime_t (and timer) down into the derived fence > class, but I think there is going to need to be some extra storage > *somewhere*.. maybe the fence signaler could get away with just > storing the nearest upcoming deadline per fence-context instead? I would just push that into the driver instead. You most likely don't want the deadline per fence anyway in complex scenarios, but rather per frame. And a frame is usually composed from multiple fences. Regards, Christian. > > BR, > -R > >> 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);