[Intel-xe] [PATCH 4/8] drm/sched: Add generic scheduler message interface
Christian König
christian.koenig at amd.com
Mon Aug 7 15:46:16 UTC 2023
Am 04.08.23 um 16:13 schrieb Matthew Brost:
> [SNIP]
> Christian / Daniel - I've read both of you comments and having a hard
> time parsing them. I do not really understand the issue with this patch
> or exactly what is being suggested instead. Let's try to work through
> this.
>
>>>>> I'm still extremely frowned on this.
>>>>>
>>>>> If you need this functionality then let the drivers decide which
>>>>> runqueue the scheduler should use.
> What do you mean by runqueue here? Do you mean 'struct
> workqueue_struct'? The scheduler in this context is 'struct
> drm_gpu_scheduler', right?
Sorry for the confusing wording, your understanding is correct.
> Yes, we have added this functionality iin the first patch.
>
>>>>> When you then create a single threaded runqueue you can just submit work
>>>>> to it and serialize this with the scheduler work.
>>>>>
> We don't want to use a single threaded workqueue_struct in Xe, we want
> to use a system_wq as run_job() can be executed in parallel across
> multiple entites (or drm_gpu_scheduler as in Xe we have 1 to 1
> relationship between entity and scheduler). What we want is on per
> entity / scheduler granularity to be able to communicate into the
> backend a message synchronously (run_job / free_job not executing,
> scheduler execution not paused for a reset).
>
> If I'm underatanding what you suggesting in Xe we'd create an ordered
> workqueue_struct per drm_gpu_scheduler and the queue messages on the
> ordered workqueue_struct?
Yes, correct.
> This seems pretty messy to me as now we have
> open coded a solution bypassing the scheduler, every drm_gpu_scheduler
> creates its own workqueue_struct, and we'd also have to open code the
> pausing of these messages for resets too.
>
> IMO this is pretty clean solution that follows the pattern of cleanup
> jobs already in place.
Yeah, exactly that's the point. Moving the job cleanup into the
scheduler thread is seen as very very bad idea by me.
And I really don't want to exercise that again for different use cases.
>
>>>>> This way we wouldn't duplicate this core kernel function inside the
>>>>> scheduler.
>>>> Yeah that's essentially the design we picked for the tdr workers,
>>>> where some drivers have requirements that all tdr work must be done on
>>>> the same thread (because of cross-engine coordination issues). But
>>>> that would require that we rework the scheduler as a pile of
>>>> self-submitting work items, and I'm not sure that actually fits all
>>>> that well into the core workqueue interfaces either.
> This is the ordering between TDRs firing between different
> drm_gpu_scheduler and larger external resets (GT in Xe) an ordered
> workqueue_struct makes sense for this. Here we are talking about
> ordering jobs and messages within a single drm_gpu_scheduler. Using the
> main execution thread to do ordering makes sense in my opinion.
I completely disagree to that.
Take a look at how this came to be. This is a very very ugly hack and we
already had a hard time making lockdep understand the different fence
signaling dependencies with freeing the job and I'm pretty sure that is
still not 100% correct.
>
>>> There were already patches floating around which did exactly that.
>>>
>>> Last time I checked those were actually looking pretty good.
>>>
> Link to patches for reference.
>
>>> Additional to message passing advantage the real big issue with the
>>> scheduler and 1 to 1 mapping is that we create a kernel thread for each
>>> instance, which results in tons on overhead.
> First patch in the series switches from kthread to work queue, that is
> still a good idea.
This was the patch I was referring to. Sorry didn't remembered that this
was in the same patch set.
>
>>> Just using a work item which is submitted to a work queue completely avoids
>>> that.
>> Hm I should have read the entire series first, since that does the
>> conversion still. Apologies for the confusion, and yeah we should be able
>> to just submit other work to the same wq with the first patch? And so
>> hand-rolling this infra here isn't needed at all?
>>
> I wouldn't call this hand rolling, rather it following patten already in
> place.
Basically workqueues are the in kernel infrastructure for exactly that
use case and we are trying to re-create that here and that is usually a
rather bad idea.
Regards,
Christian.
>
> Matt
>
>> Or what am I missing?
>>
>>> Regards,
>>> Christian.
>>>
>>>> Worst case I think this isn't a dead-end and can be refactored to
>>>> internally use the workqueue services, with the new functions here
>>>> just being dumb wrappers until everyone is converted over. So it
>>>> doesn't look like an expensive mistake, if it turns out to be a
>>>> mistake.
>>>> -Daniel
>>>>
>>>>
>>>>> Regards,
>>>>> Christian.
>>>>>
>>>>>> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
>>>>>> ---
>>>>>> drivers/gpu/drm/scheduler/sched_main.c | 52 +++++++++++++++++++++++++-
>>>>>> include/drm/gpu_scheduler.h | 29 +++++++++++++-
>>>>>> 2 files changed, 78 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>>>>>> index 2597fb298733..84821a124ca2 100644
>>>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>>>> @@ -1049,6 +1049,49 @@ drm_sched_pick_best(struct drm_gpu_scheduler **sched_list,
>>>>>> }
>>>>>> EXPORT_SYMBOL(drm_sched_pick_best);
>>>>>>
>>>>>> +/**
>>>>>> + * drm_sched_add_msg - add scheduler message
>>>>>> + *
>>>>>> + * @sched: scheduler instance
>>>>>> + * @msg: message to be added
>>>>>> + *
>>>>>> + * Can and will pass an jobs waiting on dependencies or in a runnable queue.
>>>>>> + * Messages processing will stop if schedule run wq is stopped and resume when
>>>>>> + * run wq is started.
>>>>>> + */
>>>>>> +void drm_sched_add_msg(struct drm_gpu_scheduler *sched,
>>>>>> + struct drm_sched_msg *msg)
>>>>>> +{
>>>>>> + spin_lock(&sched->job_list_lock);
>>>>>> + list_add_tail(&msg->link, &sched->msgs);
>>>>>> + spin_unlock(&sched->job_list_lock);
>>>>>> +
>>>>>> + drm_sched_run_wq_queue(sched);
>>>>>> +}
>>>>>> +EXPORT_SYMBOL(drm_sched_add_msg);
>>>>>> +
>>>>>> +/**
>>>>>> + * drm_sched_get_msg - get scheduler message
>>>>>> + *
>>>>>> + * @sched: scheduler instance
>>>>>> + *
>>>>>> + * Returns NULL or message
>>>>>> + */
>>>>>> +static struct drm_sched_msg *
>>>>>> +drm_sched_get_msg(struct drm_gpu_scheduler *sched)
>>>>>> +{
>>>>>> + struct drm_sched_msg *msg;
>>>>>> +
>>>>>> + spin_lock(&sched->job_list_lock);
>>>>>> + msg = list_first_entry_or_null(&sched->msgs,
>>>>>> + struct drm_sched_msg, link);
>>>>>> + if (msg)
>>>>>> + list_del(&msg->link);
>>>>>> + spin_unlock(&sched->job_list_lock);
>>>>>> +
>>>>>> + return msg;
>>>>>> +}
>>>>>> +
>>>>>> /**
>>>>>> * drm_sched_main - main scheduler thread
>>>>>> *
>>>>>> @@ -1060,6 +1103,7 @@ static void drm_sched_main(struct work_struct *w)
>>>>>> container_of(w, struct drm_gpu_scheduler, work_run);
>>>>>> struct drm_sched_entity *entity;
>>>>>> struct drm_sched_job *cleanup_job;
>>>>>> + struct drm_sched_msg *msg;
>>>>>> int r;
>>>>>>
>>>>>> if (READ_ONCE(sched->pause_run_wq))
>>>>>> @@ -1067,12 +1111,15 @@ static void drm_sched_main(struct work_struct *w)
>>>>>>
>>>>>> cleanup_job = drm_sched_get_cleanup_job(sched);
>>>>>> entity = drm_sched_select_entity(sched);
>>>>>> + msg = drm_sched_get_msg(sched);
>>>>>>
>>>>>> - if (!entity && !cleanup_job)
>>>>>> + if (!entity && !cleanup_job && !msg)
>>>>>> return; /* No more work */
>>>>>>
>>>>>> if (cleanup_job)
>>>>>> sched->ops->free_job(cleanup_job);
>>>>>> + if (msg)
>>>>>> + sched->ops->process_msg(msg);
>>>>>>
>>>>>> if (entity) {
>>>>>> struct dma_fence *fence;
>>>>>> @@ -1082,7 +1129,7 @@ static void drm_sched_main(struct work_struct *w)
>>>>>> sched_job = drm_sched_entity_pop_job(entity);
>>>>>> if (!sched_job) {
>>>>>> complete_all(&entity->entity_idle);
>>>>>> - if (!cleanup_job)
>>>>>> + if (!cleanup_job && !msg)
>>>>>> return; /* No more work */
>>>>>> goto again;
>>>>>> }
>>>>>> @@ -1177,6 +1224,7 @@ int drm_sched_init(struct drm_gpu_scheduler *sched,
>>>>>>
>>>>>> init_waitqueue_head(&sched->job_scheduled);
>>>>>> INIT_LIST_HEAD(&sched->pending_list);
>>>>>> + INIT_LIST_HEAD(&sched->msgs);
>>>>>> spin_lock_init(&sched->job_list_lock);
>>>>>> atomic_set(&sched->hw_rq_count, 0);
>>>>>> INIT_DELAYED_WORK(&sched->work_tdr, drm_sched_job_timedout);
>>>>>> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
>>>>>> index df1993dd44ae..267bd060d178 100644
>>>>>> --- a/include/drm/gpu_scheduler.h
>>>>>> +++ b/include/drm/gpu_scheduler.h
>>>>>> @@ -394,6 +394,23 @@ enum drm_gpu_sched_stat {
>>>>>> DRM_GPU_SCHED_STAT_ENODEV,
>>>>>> };
>>>>>>
>>>>>> +/**
>>>>>> + * struct drm_sched_msg - an in-band (relative to GPU scheduler run queue)
>>>>>> + * message
>>>>>> + *
>>>>>> + * Generic enough for backend defined messages, backend can expand if needed.
>>>>>> + */
>>>>>> +struct drm_sched_msg {
>>>>>> + /** @link: list link into the gpu scheduler list of messages */
>>>>>> + struct list_head link;
>>>>>> + /**
>>>>>> + * @private_data: opaque pointer to message private data (backend defined)
>>>>>> + */
>>>>>> + void *private_data;
>>>>>> + /** @opcode: opcode of message (backend defined) */
>>>>>> + unsigned int opcode;
>>>>>> +};
>>>>>> +
>>>>>> /**
>>>>>> * struct drm_sched_backend_ops - Define the backend operations
>>>>>> * called by the scheduler
>>>>>> @@ -471,6 +488,12 @@ struct drm_sched_backend_ops {
>>>>>> * and it's time to clean it up.
>>>>>> */
>>>>>> void (*free_job)(struct drm_sched_job *sched_job);
>>>>>> +
>>>>>> + /**
>>>>>> + * @process_msg: Process a message. Allowed to block, it is this
>>>>>> + * function's responsibility to free message if dynamically allocated.
>>>>>> + */
>>>>>> + void (*process_msg)(struct drm_sched_msg *msg);
>>>>>> };
>>>>>>
>>>>>> /**
>>>>>> @@ -482,6 +505,7 @@ struct drm_sched_backend_ops {
>>>>>> * @timeout: the time after which a job is removed from the scheduler.
>>>>>> * @name: name of the ring for which this scheduler is being used.
>>>>>> * @sched_rq: priority wise array of run queues.
>>>>>> + * @msgs: list of messages to be processed in @work_run
>>>>>> * @job_scheduled: once @drm_sched_entity_do_release is called the scheduler
>>>>>> * waits on this wait queue until all the scheduled jobs are
>>>>>> * finished.
>>>>>> @@ -489,7 +513,7 @@ struct drm_sched_backend_ops {
>>>>>> * @job_id_count: used to assign unique id to the each job.
>>>>>> * @run_wq: workqueue used to queue @work_run
>>>>>> * @timeout_wq: workqueue used to queue @work_tdr
>>>>>> - * @work_run: schedules jobs and cleans up entities
>>>>>> + * @work_run: schedules jobs, cleans up jobs, and processes messages
>>>>>> * @work_tdr: schedules a delayed call to @drm_sched_job_timedout after the
>>>>>> * timeout interval is over.
>>>>>> * @pending_list: the list of jobs which are currently in the job queue.
>>>>>> @@ -513,6 +537,7 @@ struct drm_gpu_scheduler {
>>>>>> long timeout;
>>>>>> const char *name;
>>>>>> struct drm_sched_rq sched_rq[DRM_SCHED_PRIORITY_COUNT];
>>>>>> + struct list_head msgs;
>>>>>> wait_queue_head_t job_scheduled;
>>>>>> atomic_t hw_rq_count;
>>>>>> atomic64_t job_id_count;
>>>>>> @@ -566,6 +591,8 @@ void drm_sched_entity_modify_sched(struct drm_sched_entity *entity,
>>>>>>
>>>>>> void drm_sched_job_cleanup(struct drm_sched_job *job);
>>>>>> void drm_sched_wakeup(struct drm_gpu_scheduler *sched);
>>>>>> +void drm_sched_add_msg(struct drm_gpu_scheduler *sched,
>>>>>> + struct drm_sched_msg *msg);
>>>>>> void drm_sched_run_wq_stop(struct drm_gpu_scheduler *sched);
>>>>>> void drm_sched_run_wq_start(struct drm_gpu_scheduler *sched);
>>>>>> void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad);
>> --
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> http://blog.ffwll.ch
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