Hi Danilo, On Thu, 26 Oct 2023 18:13:00 +0200 Danilo Krummrich <dakr@xxxxxxxxxx> wrote: > Currently, job flow control is implemented simply by limiting the number > of jobs in flight. Therefore, a scheduler is initialized with a credit > limit that corresponds to the number of jobs which can be sent to the > hardware. > > This implies that for each job, drivers need to account for the maximum > job size possible in order to not overflow the ring buffer. > > However, there are drivers, such as Nouveau, where the job size has a > rather large range. For such drivers it can easily happen that job > submissions not even filling the ring by 1% can block subsequent > submissions, which, in the worst case, can lead to the ring run dry. > > In order to overcome this issue, allow for tracking the actual job size > instead of the number of jobs. Therefore, add a field to track a job's > credit count, which represents the number of credits a job contributes > to the scheduler's credit limit. > > Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx> > --- > Changes in V2: > ============== > - fixed up influence on scheduling fairness due to consideration of a job's > size > - If we reach a ready entity in drm_sched_select_entity() but can't actually > queue a job from it due to size limitations, just give up and go to sleep > until woken up due to a pending job finishing, rather than continue to try > other entities. > - added a callback to dynamically update a job's credits (Boris) This callback seems controversial. I'd suggest dropping it, so the patch can be merged. Regards, Boris > - renamed 'units' to 'credits' > - fixed commit message and comments as requested by Luben > > Changes in V3: > ============== > - rebased onto V7 of the "DRM scheduler changes for Xe" series by Matt > - move up drm_sched_can_queue() instead of adding a forward declaration > (Boris) > - add a drm_sched_available_credits() helper (Boris) > - adjust control flow in drm_sched_rq_select_entity_fifo() to Luben's proposal > - re-phrase a few comments and fix a typo (Luben) > - change naming of all structures credit fields and function parameters to the > following scheme > - drm_sched_job::credits > - drm_gpu_scheduler::credit_limit > - drm_gpu_scheduler::credit_count > - drm_sched_init(..., u32 credit_limit, ...) > - drm_sched_job_init(..., u32 credits, ...) > - add proper documentation for the scheduler's job-flow control mechanism
