On Tue, Apr 04, 2023 at 12:02:03PM -0600, Zeng, Oak wrote: > Hi Matt, Thomas, > > Some very bold out of box thinking in this area: > > 1. so you want to use drm scheduler and dma-fence for long running workload. > Why you want to do this in the first place? What is the benefit? Drm > scheduler is pretty much a software scheduler. Modern gpu has scheduler built > at fw/hw level, as you said below for intel this is Guc. Can xe driver just > directly submit job to Guc, bypassing drm scheduler? >
If we did that now we have 2 paths for dependency track, flow controling the ring, resets / error handling / backend submission implementations. We don't want this. > 2. using dma-fence for long run workload: I am well aware that page fault > (and the consequent memory allocation/lock acquiring to fix the fault) can > cause deadlock for a dma-fence wait. But I am not convinced that dma-fence > can't be used purely because the nature of the workload that it runs very > long (indefinite). I did a math: the dma_fence_wait_timeout function's third > param is the timeout which is a signed long type. If HZ is 1000, this is > about 23 days. If 23 days is not long enough, can we just change the timeout > parameter to signed 64 bits so it is much longer than our life time... > > So I mainly argue we can't use dma-fence for long-run workload is not because > the workload runs very long, rather because of the fact that we use page > fault for long-run workload. If we enable page fault for short-run workload, > we can't use dma-fence either. Page fault is the key thing here. > > Now since we use page fault which is *fundamentally* controversial with > dma-fence design, why now just introduce a independent concept such as > user-fence instead of extending existing dma-fence? > > I like unified design. If drm scheduler, dma-fence can be extended to work > for everything, it is beautiful. But seems we have some fundamental problem > here. > Thomas's patches turn a dma-fence into KMD sync point (e.g. we just use the signal / CB infrastructure) and enforce we don't use use these dma-fences from the scheduler in memory reclaim paths or export these to user space or other drivers. Think of this mode as SW only fence. Matt > Thanks, > Oak > > > -----Original Message----- > > From: dri-devel <dri-devel-boun...@lists.freedesktop.org> On Behalf Of > > Matthew Brost > > Sent: April 3, 2023 8:22 PM > > To: dri-devel@lists.freedesktop.org; intel...@lists.freedesktop.org > > Cc: robdcl...@chromium.org; thomas.hellst...@linux.intel.com; > > airl...@linux.ie; > > l...@asahilina.net; boris.brezil...@collabora.com; Brost, Matthew > > <matthew.br...@intel.com>; christian.koe...@amd.com; > > faith.ekstr...@collabora.com > > Subject: [RFC PATCH 00/10] Xe DRM scheduler and long running workload plans > > > > Hello, > > > > As a prerequisite to merging the new Intel Xe DRM driver [1] [2], we > > have been asked to merge our common DRM scheduler patches first as well > > as develop a common solution for long running workloads with the DRM > > scheduler. This RFC series is our first attempt at doing this. We > > welcome any and all feedback. > > > > This can we thought of as 4 parts detailed below. > > > > - DRM scheduler changes for 1 to 1 relationship between scheduler and > > entity (patches 1-3) > > > > In Xe all of the scheduling of jobs is done by a firmware scheduler (the > > GuC) which is a new paradigm WRT to the DRM scheduler and presents > > severals problems as the DRM was originally designed to schedule jobs on > > hardware queues. The main problem being that DRM scheduler expects the > > submission order of jobs to be the completion order of jobs even across > > multiple entities. This assumption falls apart with a firmware scheduler > > as a firmware scheduler has no concept of jobs and jobs can complete out > > of order. A novel solution for was originally thought of by Faith during > > the initial prototype of Xe, create a 1 to 1 relationship between scheduler > > and entity. I believe the AGX driver [3] is using this approach and > > Boris may use approach as well for the Mali driver [4]. > > > > To support a 1 to 1 relationship we move the main execution function > > from a kthread to a work queue and add a new scheduling mode which > > bypasses code in the DRM which isn't needed in a 1 to 1 relationship. > > The new scheduling mode should unify all drivers usage with a 1 to 1 > > relationship and can be thought of as using scheduler as a dependency / > > infligt job tracker rather than a true scheduler. > > > > - Generic messaging interface for DRM scheduler > > > > Idea is to be able to communicate to the submission backend with in band > > (relative to main execution function) messages. Messages are backend > > defined and flexable enough for any use case. In Xe we use these > > messages to clean up entites, set properties for entites, and suspend / > > resume execution of an entity [5]. I suspect other driver can leverage > > this messaging concept too as it a convenient way to avoid races in the > > backend. > > > > - Support for using TDR for all error paths of a scheduler / entity > > > > Fix a few races / bugs, add function to dynamically set the TDR timeout. > > > > - Annotate dma-fences for long running workloads. > > > > The idea here is to use dma-fences only as sync points within the > > scheduler and never export them for long running workloads. By > > annotating these fences as long running we ensure that these dma-fences > > are never used in a way that breaks the dma-fence rules. A benefit of > > thus approach is the scheduler can still safely flow control the > > execution ring buffer via the job limit without breaking the dma-fence > > rules. > > > > Again this a first draft and looking forward to feedback. > > > > Enjoy - Matt > > > > [1] https://gitlab.freedesktop.org/drm/xe/kernel > > [2] https://patchwork.freedesktop.org/series/112188/ > > [3] https://patchwork.freedesktop.org/series/114772/ > > [4] https://patchwork.freedesktop.org/patch/515854/?series=112188&rev=1 > > [5] https://gitlab.freedesktop.org/drm/xe/kernel/-/blob/drm-xe- > > next/drivers/gpu/drm/xe/xe_guc_submit.c#L1031 > > > > Matthew Brost (8): > > drm/sched: Convert drm scheduler to use a work queue rather than > > kthread > > drm/sched: Move schedule policy to scheduler / entity > > drm/sched: Add DRM_SCHED_POLICY_SINGLE_ENTITY scheduling policy > > drm/sched: Add generic scheduler message interface > > drm/sched: Start run wq before TDR in drm_sched_start > > drm/sched: Submit job before starting TDR > > drm/sched: Add helper to set TDR timeout > > drm/syncobj: Warn on long running dma-fences > > > > Thomas Hellström (2): > > dma-buf/dma-fence: Introduce long-running completion fences > > drm/sched: Support long-running sched entities > > > > drivers/dma-buf/dma-fence.c | 142 +++++++--- > > drivers/dma-buf/dma-resv.c | 5 + > > drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c | 14 +- > > drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 15 +- > > drivers/gpu/drm/drm_syncobj.c | 5 +- > > drivers/gpu/drm/etnaviv/etnaviv_sched.c | 5 +- > > drivers/gpu/drm/lima/lima_sched.c | 5 +- > > drivers/gpu/drm/msm/adreno/adreno_device.c | 6 +- > > drivers/gpu/drm/msm/msm_ringbuffer.c | 5 +- > > drivers/gpu/drm/panfrost/panfrost_job.c | 5 +- > > drivers/gpu/drm/scheduler/sched_entity.c | 127 +++++++-- > > drivers/gpu/drm/scheduler/sched_fence.c | 6 +- > > drivers/gpu/drm/scheduler/sched_main.c | 278 +++++++++++++++----- > > drivers/gpu/drm/v3d/v3d_sched.c | 25 +- > > include/drm/gpu_scheduler.h | 130 +++++++-- > > include/linux/dma-fence.h | 60 ++++- > > 16 files changed, 649 insertions(+), 184 deletions(-) > > > > -- > > 2.34.1 >
