diff options
Diffstat (limited to 'drivers/dma-buf/dma-fence.c')
| -rw-r--r-- | drivers/dma-buf/dma-fence.c | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c index 0de0482cd36e..f177c56269bb 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -913,6 +913,65 @@ err_free_cb: EXPORT_SYMBOL(dma_fence_wait_any_timeout); /** + * DOC: deadline hints + * + * In an ideal world, it would be possible to pipeline a workload sufficiently + * that a utilization based device frequency governor could arrive at a minimum + * frequency that meets the requirements of the use-case, in order to minimize + * power consumption. But in the real world there are many workloads which + * defy this ideal. For example, but not limited to: + * + * * Workloads that ping-pong between device and CPU, with alternating periods + * of CPU waiting for device, and device waiting on CPU. This can result in + * devfreq and cpufreq seeing idle time in their respective domains and in + * result reduce frequency. + * + * * Workloads that interact with a periodic time based deadline, such as double + * buffered GPU rendering vs vblank sync'd page flipping. In this scenario, + * missing a vblank deadline results in an *increase* in idle time on the GPU + * (since it has to wait an additional vblank period), sending a signal to + * the GPU's devfreq to reduce frequency, when in fact the opposite is what is + * needed. + * + * To this end, deadline hint(s) can be set on a &dma_fence via &dma_fence_set_deadline. + * The deadline hint provides a way for the waiting driver, or userspace, to + * convey an appropriate sense of urgency to the signaling driver. + * + * A deadline hint is given in absolute ktime (CLOCK_MONOTONIC for userspace + * facing APIs). The time could either be some point in the future (such as + * the vblank based deadline for page-flipping, or the start of a compositor's + * composition cycle), or the current time to indicate an immediate deadline + * hint (Ie. forward progress cannot be made until this fence is signaled). + * + * Multiple deadlines may be set on a given fence, even in parallel. See the + * documentation for &dma_fence_ops.set_deadline. + * + * The deadline hint is just that, a hint. The driver that created the fence + * may react by increasing frequency, making different scheduling choices, etc. + * Or doing nothing at all. + */ + +/** + * dma_fence_set_deadline - set desired fence-wait deadline hint + * @fence: the fence that is to be waited on + * @deadline: the time by which the waiter hopes for the fence to be + * signaled + * + * Give the fence signaler a hint about 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 but the fence is not + * yet signaled.. + */ +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_describe - Dump fence describtion into seq_file * @fence: the 6fence to describe * @seq: the seq_file to put the textual description into |