| Message ID | 20210903184806.1680887-1-robdclark@gmail.com |
|---|---|
| Headers | show |
| Series | dma-fence: Deadline awareness | expand |
Out of curiosity, would it be reasonable to allow user-space (more precisely, the compositor) to set the deadline via an IOCTL without actually performing an atomic commit with the FB? Some compositors might want to wait themselves for FB fence completions to ensure a client doesn't block the whole desktop (by submitting a very costly rendering job). In this case it would make sense for the compositor to indicate that it intends to display the buffer on next vblank if it's ready by that point, without queueing a page-flip yet.
On Thu, Sep 9, 2021 at 9:16 AM Simon Ser <contact@emersion.fr> wrote: > > Out of curiosity, would it be reasonable to allow user-space (more > precisely, the compositor) to set the deadline via an IOCTL without > actually performing an atomic commit with the FB? > > Some compositors might want to wait themselves for FB fence completions > to ensure a client doesn't block the whole desktop (by submitting a > very costly rendering job). In this case it would make sense for the > compositor to indicate that it intends to display the buffer on next > vblank if it's ready by that point, without queueing a page-flip yet. Yes, I think it would.. and "dma-buf/sync_file: Add SET_DEADLINE ioctl" adds such an ioctl.. just for the benefit of igt tests at this point, but the thought was it would be also used by compositors that are doing such frame scheduling. Ofc danvet is a bit grumpy that there isn't a more real (than igt) userspace for the ioctl yet ;-) BR, -R
On Thursday, September 9th, 2021 at 18:31, Rob Clark <robdclark@gmail.com> wrote: > Yes, I think it would.. and "dma-buf/sync_file: Add SET_DEADLINE > ioctl" adds such an ioctl.. just for the benefit of igt tests at this > point, but the thought was it would be also used by compositors that > are doing such frame scheduling. Ofc danvet is a bit grumpy that > there isn't a more real (than igt) userspace for the ioctl yet ;-) Ah, very nice, I somehow missed it. I guess one issue is that explicit sync isn't quite plumbed through compositors yet, so without Jason's DMA-BUF to sync_file IOCTL it'd be a bit difficult to use. Can anybody set the deadline? I wonder if clients should be allowed to. What happens if the deadline is exceeded? I'd assume nothing in particular, the deadline being just a hint?
On Thu, Sep 9, 2021 at 9:42 AM Simon Ser <contact@emersion.fr> wrote: > > On Thursday, September 9th, 2021 at 18:31, Rob Clark <robdclark@gmail.com> wrote: > > > Yes, I think it would.. and "dma-buf/sync_file: Add SET_DEADLINE > > ioctl" adds such an ioctl.. just for the benefit of igt tests at this > > point, but the thought was it would be also used by compositors that > > are doing such frame scheduling. Ofc danvet is a bit grumpy that > > there isn't a more real (than igt) userspace for the ioctl yet ;-) > > Ah, very nice, I somehow missed it. > > I guess one issue is that explicit sync isn't quite plumbed through > compositors yet, so without Jason's DMA-BUF to sync_file IOCTL it'd be > a bit difficult to use. > > Can anybody set the deadline? I wonder if clients should be allowed to. In its current form, anyone who has the fd can.. I'm not sure how (or even if) we could limit it beyond that. I suppose hypothetically you could use this for completely non-compositor related things, like compute jobs where you want the result by some deadline. (OTOH, it could be the driver using this internally when the app is stalling on a result) > What happens if the deadline is exceeded? I'd assume nothing in > particular, the deadline being just a hint? Nothing in particular, it is just a hint. The main intention is to provide a feedback hint to the drivers in scenarios like vblank deadlines, where being 1ms late is just as bad as being $frame_duration-1ms late. From my experiments and profiling it is useful in a couple scenarios: 1) input latency, ie. go from idle to fullscreen animation, where GPU has been idle for a while and not busy enough *yet* for devfreq to kick in and start ramping up the freq before we miss the first vblank 2) double buffering, for ex. if you are 1ms late you end up stalling 15ms before the gpu can start rendering the next frame.. in the absence of feedback, devfreq would ramp down in this scenario instead of up BR, -R
From: Rob Clark <robdclark@chromium.org> This series adds deadline awareness to fences, so realtime deadlines such as vblank can be communicated to the fence signaller for power/ frequency management decisions. This is partially inspired by a trick i915 does, but implemented via dma-fence for a couple of reasons: 1) To continue to be able to use the atomic helpers 2) To support cases where display and gpu are different drivers This iteration adds a dma-fence ioctl to set a deadline (both to support igt-tests, and compositors which delay decisions about which client buffer to display), and a sw_sync ioctl to read back the deadline. IGT tests utilizing these can be found at: https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadline v1: https://patchwork.freedesktop.org/series/93035/ v2: Move filtering out of later deadlines to fence implementation to avoid increasing the size of dma_fence v3: Add support in fence-array and fence-chain; Add some uabi to support igt tests and userspace compositors. Rob Clark (9): dma-fence: Add deadline awareness drm/vblank: Add helper to get next vblank time drm/atomic-helper: Set fence deadline for vblank drm/scheduler: Add fence deadline support drm/msm: Add deadline based boost support dma-buf/fence-array: Add fence deadline support dma-buf/fence-chain: Add fence deadline support dma-buf/sync_file: Add SET_DEADLINE ioctl dma-buf/sw_sync: Add fence deadline support drivers/dma-buf/dma-fence-array.c | 11 ++++ drivers/dma-buf/dma-fence-chain.c | 13 +++++ drivers/dma-buf/dma-fence.c | 20 +++++++ drivers/dma-buf/sw_sync.c | 58 +++++++++++++++++++ drivers/dma-buf/sync_debug.h | 2 + drivers/dma-buf/sync_file.c | 19 +++++++ drivers/gpu/drm/drm_atomic_helper.c | 36 ++++++++++++ drivers/gpu/drm/drm_vblank.c | 32 +++++++++++ drivers/gpu/drm/msm/msm_fence.c | 76 +++++++++++++++++++++++++ drivers/gpu/drm/msm/msm_fence.h | 20 +++++++ drivers/gpu/drm/msm/msm_gpu.h | 1 + drivers/gpu/drm/msm/msm_gpu_devfreq.c | 20 +++++++ drivers/gpu/drm/scheduler/sched_fence.c | 34 +++++++++++ drivers/gpu/drm/scheduler/sched_main.c | 2 +- include/drm/drm_vblank.h | 1 + include/drm/gpu_scheduler.h | 8 +++ include/linux/dma-fence.h | 16 ++++++ include/uapi/linux/sync_file.h | 20 +++++++ 18 files changed, 388 insertions(+), 1 deletion(-)