On Wed, 2025-10-08 at 09:53 +0100, Tvrtko Ursulin wrote: > [disclaimer] > Please note that as this series includes patches which touch a good number of > drivers, I did not copy everyone on everything. Assumption is people are > subscribed to dri-devel and for context can look at the whole series there. > [/disclaimer] > > As a summary, the new scheduling algorithm is insipired by the original Linux > CFS and so far no scheduling regressions have been found relative to FIFO. > There are improvements in fairness and scheduling of interactive clients when > running in parallel with a heavy GPU load (for example Pierre-Eric has one > viewperf medical test which shows a nice improvement with amdgpu). > > On the high level main advantages of the series are: > > 1. Scheduling quality - schedules better than FIFO, solves priority > starvation. > 2. Code simplification - no more multiple run queues and multiple algorithms. > 3. Virtual GPU time based scheduling enables relatively simple addition > of a scheduling cgroup controller in the future. > > There is a little bit more detailed write up on the motivation and results in > the form of a blog post which may be easier to read: > https://blogs.igalia.com/tursulin/fair-er-drm-gpu-scheduler/ > > First patches add some unit tests which allow for easy evaluation of > scheduling > behaviour against different client submission patterns. From there onwards it > is > hopefully a natural progression of cleanups, enablers, adding the fair policy, > and finally removing FIFO and RR and simplifying the code base due no more > need > for multiple run queues. > > Series is structured in a way where we could apply the first 12 patches (up to > and including "drm/sched: Switch default policy to fair") in one kernel > release > and then follow up with the rest of the cleanups after a release or two if > things will be looking fine. Until the remainder of the series would be merged > it would be easy to flip the default algorithm back. > > Onto the performance evaluation. As a headline result I have tested three > simultaneous clients on the Steam Deck: > > One instance of a deferredmultisampling Vulkan demo running with low priority, > one normal priority instance of the same demo, and the Unigine Heaven > benchmark. > > With the FIFO scheduler we can see that the low priority client is completely > starved and the GPU time distribution between the other two clients is uneven: > > https://people.igalia.com/tursulin/drm-sched-fair/fifo-starvation.png > > Switching to the fair scheduler, GPU time distribution is almost equal and the > low priority client does get a small share of the GPU: > > https://people.igalia.com/tursulin/drm-sched-fair/fair-no-starvation.png > > Moving onto the synthetic submission patterns, they are about two simultaneous > clients which broadly cover the following categories: > > * Deep queue clients > * Hogs versus interactive > * Priority handling > > Lets look at the results: > > 1. Two normal priority deep queue clients. > > These ones submit one second worth of 8ms jobs. As fast as they can, no > dependencies etc. There is no difference in runtime between FIFO and fair but > the latter allows both clients to progress with work more evenly: > > https://people.igalia.com/tursulin/drm-sched-fair/normal-normal.png > > (X axis is time, Y is submitted queue-depth, hence lowering of qd corresponds > with work progress for both clients, tested with both schedulers > separately.) > > Round-robin is the same as fair here. > > 2. Same two clients but one is now low priority. > > https://people.igalia.com/tursulin/drm-sched-fair/normal-low.png > > Normal priority client is a solid line, low priority dotted. We can see how > FIFO > completely starves the low priority client until the normal priority is fully > done. Only then the low priority client gets any GPU time. > > In constrast, fair scheduler allows some GPU time to the low priority client. > > Here round-robin flavours are the same as FIFO (same starvation issue). > > 3. Same clients but now high versus normal priority. > > Similar behaviour as in the previous one with normal a bit less de-prioritised > relative to high, than low was against normal. > > https://people.igalia.com/tursulin/drm-sched-fair/high-normal.png > > And again round-robin flavours are the same as FIFO. > > 4. Heavy load vs interactive client. > > Heavy client emits a 75% GPU load in the format of 3x 2.5ms jobs followed by a > 2.5ms wait. Interactive client emits a 10% GPU load in the format of 1x 1ms > job > followed by a 9ms wait. > > This simulates an interactive graphical client used on top of a relatively > heavy > background load but no GPU oversubscription. > > Graphs show the interactive client only and from now on, instead of looking at > the client's queue depth, we look at its "fps". > > https://people.igalia.com/tursulin/drm-sched-fair/251008/4-heavy-vs-interactive.png > > Here round-robin and round-robin rewritten on top of FIFO are best, with the > fair algorithm being very close. FIFO is clearly the worst. > > 5. An even heavier load vs interactive client. > > This one is oversubscribing the GPU by submitting 4x 50ms jobs and waiting for > only one microsecond before repeating the cycle. Interactive client is the > same > 10% as above. > > https://people.igalia.com/tursulin/drm-sched-fair/251008/4-very-heavy-vs-interactive.png > > Here FIFO is even worse and fair is again almost as good as the two > round-robin > flavours. > > 6. Low priority GPU hog versus heavy-interactive. > > Low priority client: 3x 2.5ms jobs client followed by a 0.5ms wait. > Interactive client: 1x 0.5ms job followed by a 10ms wait. > > https://people.igalia.com/tursulin/drm-sched-fair/251008/4-low-hog-vs-interactive.png > > All schedulers appear to handle this almost equally well but FIFO could still > be > the last while fair has a slight lead. > > As before, I am looking for feedback, ideas for what other kinds of submission > scenarios to test, testing on different GPUs and of course reviews. > > v2: > * Fixed many rebase errors. > * Added some new patches. > * Dropped single shot dependecy handling. > > v3: > * Added scheduling quality unit tests. > * Refined a tiny bit by adding some fairness. > * Dropped a few patches for now. > > v4: > * Replaced deadline with fair! > * Refined scheduling quality unit tests. > * Pulled one cleanup patch earlier. > * Fixed "drm/sched: Avoid double re-lock on the job free path". > > v5: > * Rebase on top of latest upstream DRM scheduler changes. > * Kerneldoc fixup. > * Improve commit message justification for one patch. (Philipp) > * Add comment in drm_sched_alloc_wq. (Christian) > > v6: > * Rebase for "drm/sched: De-clutter drm_sched_init" getting merged. > * Avoid NULL rq dereference from a bad rebase. (Maira) > * Added some kerneldoc throughout. (Maira) > * Removed some lockdep annotations not belonging to one patch. (Maira) > * Use dma_fence_is_signaled in "drm/sched: Avoid double re-lock on the job > free path". (Maira, Philipp) > > v7: > * Rebase for some prep patches getting merged. > * Dropped submit all ready jobs patch. > * Fixed 64-bit division in unit tests. > * Fixed some more rebase and patch re-ordering mistakes. > * Preserve entity RR order when re-entering the queue. > * Fine tuned the queue re-enter logic for better behaviour with interactive > clients. > * Removed some static inlines. > * Added more kerneldoc. > * Done some benchmarks in the round-robin scheduling modes. > > v8: > * Rebased for upstream changes. > * Added assert for reverse numerical order of DRM_SCHED_PRIORITY enums. > * Fixed head of rq priority updates. > > v9: > * RFC -> PATCH for the series as agreed during the XDC.
So this is not v9 of an RFC, but v1 of the actual series :) I think you wanna mark the old changelog section as belonging to the RFC, since this one will likely move to v2 etc., which might cause confusion. P. > * Updated interactive benchmark graphs. > * Improved handling of interactive clients by replacing the random noise on > tie > approach with the average job duration statistics. > * Document in code why we track entity GPU stats in a reference counted > structures. > * Document the new structure fields added by the fair policy. > * Undo some tab vs spaces damage. > * More accurate wording in the fair policy commit message. > * Default to fair policy in a separate patch. > * Renamed drm_sched_rq_select_entity to drm_sched_select_entity and make it > only take sched. > * Fixed kerneldoc after removing scheduling policies and renaming the rq. > * Reversed arguments of drm_sched_rq_init and cleanup callers. (New patch) > * Removed unused num_rqs from struct drm_sched_args. (New patches) > * Unit tests: > * Added wait duration comments. > * Data structure comments. > * Better name for a local variable. > * Added comment to the short job duration assert. > * Added comment for cond_resched(). > * Tweaked some comments > * Added client_done() helper and documented the READ_ONCE. > * Clarified cycles per second calculation. > > Cc: Christian König <[email protected]> > Cc: Danilo Krummrich <[email protected]> > CC: Leo Liu <[email protected]> > Cc: Matthew Brost <[email protected]> > Cc: Philipp Stanner <[email protected]> > Cc: Pierre-Eric Pelloux-Prayer <[email protected]> > Cc: Michel Dänzer <[email protected]> > > Tvrtko Ursulin (28): > drm/sched: Reverse drm_sched_rq_init arguments > drm/sched: Add some scheduling quality unit tests > drm/sched: Add some more scheduling quality unit tests > drm/sched: Implement RR via FIFO > drm/sched: Consolidate entity run queue management > drm/sched: Move run queue related code into a separate file > drm/sched: Free all finished jobs at once > drm/sched: Account entity GPU time > drm/sched: Remove idle entity from tree > drm/sched: Add fair scheduling policy > drm/sched: Favour interactive clients slightly > drm/sched: Switch default policy to fair > drm/sched: Remove FIFO and RR and simplify to a single run queue > drm/sched: Embed run queue singleton into the scheduler > accel/amdxdna: Remove drm_sched_init_args->num_rqs usage > accel/rocket: Remove drm_sched_init_args->num_rqs usage > drm/amdgpu: Remove drm_sched_init_args->num_rqs usage > drm/etnaviv: Remove drm_sched_init_args->num_rqs usage > drm/imagination: Remove drm_sched_init_args->num_rqs usage > drm/lima: Remove drm_sched_init_args->num_rqs usage > drm/msm: Remove drm_sched_init_args->num_rqs usage > drm/nouveau: Remove drm_sched_init_args->num_rqs usage > drm/panfrost: Remove drm_sched_init_args->num_rqs usage > drm/panthor: Remove drm_sched_init_args->num_rqs usage > drm/sched: Remove drm_sched_init_args->num_rqs usage > drm/v3d: Remove drm_sched_init_args->num_rqs usage > drm/xe: Remove drm_sched_init_args->num_rqs usage > drm/sched: Remove drm_sched_init_args->num_rqs > > drivers/accel/amdxdna/aie2_ctx.c | 1 - > drivers/accel/rocket/rocket_job.c | 1 - > drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 6 +- > drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 1 - > drivers/gpu/drm/amd/amdgpu/amdgpu_job.c | 27 +- > drivers/gpu/drm/amd/amdgpu/amdgpu_job.h | 5 +- > drivers/gpu/drm/amd/amdgpu/amdgpu_trace.h | 8 +- > drivers/gpu/drm/amd/amdgpu/amdgpu_vm_sdma.c | 8 +- > drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c | 8 +- > drivers/gpu/drm/etnaviv/etnaviv_sched.c | 1 - > drivers/gpu/drm/imagination/pvr_queue.c | 1 - > drivers/gpu/drm/lima/lima_sched.c | 1 - > drivers/gpu/drm/msm/msm_gem_vma.c | 1 - > drivers/gpu/drm/msm/msm_ringbuffer.c | 1 - > drivers/gpu/drm/nouveau/nouveau_sched.c | 1 - > drivers/gpu/drm/panfrost/panfrost_job.c | 1 - > drivers/gpu/drm/panthor/panthor_mmu.c | 1 - > drivers/gpu/drm/panthor/panthor_sched.c | 1 - > drivers/gpu/drm/scheduler/Makefile | 2 +- > drivers/gpu/drm/scheduler/sched_entity.c | 132 ++- > drivers/gpu/drm/scheduler/sched_fence.c | 2 +- > drivers/gpu/drm/scheduler/sched_internal.h | 99 +- > drivers/gpu/drm/scheduler/sched_main.c | 402 ++------ > drivers/gpu/drm/scheduler/sched_rq.c | 354 +++++++ > drivers/gpu/drm/scheduler/tests/Makefile | 3 +- > .../gpu/drm/scheduler/tests/mock_scheduler.c | 1 - > .../gpu/drm/scheduler/tests/tests_scheduler.c | 878 ++++++++++++++++++ > drivers/gpu/drm/v3d/v3d_sched.c | 1 - > drivers/gpu/drm/xe/xe_dep_scheduler.c | 1 - > drivers/gpu/drm/xe/xe_execlist.c | 1 - > drivers/gpu/drm/xe/xe_gpu_scheduler.c | 1 - > include/drm/gpu_scheduler.h | 43 +- > 32 files changed, 1494 insertions(+), 500 deletions(-) > create mode 100644 drivers/gpu/drm/scheduler/sched_rq.c > create mode 100644 drivers/gpu/drm/scheduler/tests/tests_scheduler.c >
