On 04/04/2023 01:22, Matthew Brost wrote:
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.
Once you add capability for a more proper 1:1 via DRM_SCHED_POLICY_SINGLE_ENTITY, do you still have further need to replace kthreads with a wq?
Or in other words, what purpose does the offloading of a job picking code to a separate execution context serve? Could it be done directly in the 1:1 mode and leave kthread setup for N:M?
Apart from those design level questions, low level open IMO still is that default fallback of using the system_wq has the potential to affect latency for other drivers. But that's for those driver owners to approve.
Regards, Tvrtko
- 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(-)
