[RFC PATCH] drm/scheduler: Set the FIFO schedulig policy as the default

[Luben Tuikov]

Yeah, it was just spelling typos. I'll add your RB to it and repost.
I cannot push to drm-misc-next, but hope someone will pick it up.

Regards,
Luben

On 2022-10-24 14:42, Christian König wrote:
> I've seen that one, but couldn't figure out what was actually changed 
> between the two.
> 
> If you just fixed a typo feel free to add my R-B to this one as well.
> 
> Christian.
> 
> Am 24.10.22 um 19:25 schrieb Luben Tuikov:
>> Hi Christian,
>>
>> Can you add an R-B to V1 of this patch, as the v1 is what I'd like pushed.
>> I sent it right after this one.
>>
>> Regards,
>> Luben
>>
>> On 2022-10-24 06:42, Christian König wrote:
>>> Am 22.10.22 um 03:09 schrieb Luben Tuikov:
>>>> The currently default Round-Robin GPU scheduling can result in starvation
>>>> of entities which have a large number of jobs, over entities which have
>>>> a very small number of jobs (single digit).
>>>>
>>>> This can be illustrated in the following diagram, where jobs are
>>>> alphabetized to show their chronological order of arrival, where job A is
>>>> the oldest, B is the second oldest, and so on, to J, the most recent job to
>>>> arrive.
>>>>
>>>>       ---> entities
>>>> j | H-F-----A--E--I--
>>>> o | --G-----B-----J--
>>>> b | --------C--------
>>>> s\/ --------D--------
>>>>
>>>> WLOG, asuming all jobs are "ready", then a R-R scheduling will execute them
>>>> in the following order (a slice off of the top of the entities' list),
>>>>
>>>> H, F, A, E, I, G, B, J, C, D.
>>>>
>>>> However, to mitigate job starvation, we'd rather execute C and D before E,
>>>> and so on, given, of course, that they're all ready to be executed.
>>>>
>>>> So, if all jobs are ready at this instant, the order of execution for this
>>>> and the next 9 instances of picking the next job to execute, should really
>>>> be,
>>>>
>>>> A, B, C, D, E, F, G, H, I, J,
>>>>
>>>> which is their chronological order. The only reason for this order to be
>>>> broken, is if an older job is not yet ready, but a younger job is ready, at
>>>> an instant of picking a new job to execute. For instance if job C wasn't
>>>> ready at time 2, but job D was ready, then we'd pick job D, like this:
>>>>
>>>> 0 +1 +2  ...
>>>> A, B, D, ...
>>>>
>>>> And from then on, C would be preferred before all other jobs, if it is ready
>>>> at the time when a new job for execution is picked. So, if C became ready
>>>> two steps later, the execution order would look like this:
>>>>
>>>> ......0 +1 +2  ...
>>>> A, B, D, E, C, F, G, H, I, J
>>>>
>>>> This is what the FIFO GPU scheduling algorithm achieves. It uses a
>>>> Red-Black tree to keep jobs sorted in chronological order, where picking
>>>> the oldest job is O(1) (we use the "cached" structure), and balancing the
>>>> tree is O(log n). IOW, it picks the *oldest ready* job to execute now.
>>>>
>>>> The implemntation is already in the kernel, and this commit only changes
>>>> the default GPU scheduling algorithm to use.
>>>>
>>>> This was tested and achieves about 1% faster performance over the Round
>>>> Robin algorithm.
>>>>
>>>> Cc: Christian König <christian.koenig at amd.com>
>>>> Cc: Alex Deucher <Alexander.Deucher at amd.com>
>>>> Cc: Direct Rendering Infrastructure - Development <dri-devel at lists.freedesktop.org>
>>>> Signed-off-by: Luben Tuikov <luben.tuikov at amd.com>
>>> Reviewed-by: Christian König <christian.koenig at amd.com>
>>>
>>>> ---
>>>>    drivers/gpu/drm/scheduler/sched_main.c | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
>>>> index 2fab218d708279..d0ff9e11cb69fa 100644
>>>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>>>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>>>> @@ -62,13 +62,13 @@
>>>>    #define to_drm_sched_job(sched_job)		\
>>>>    		container_of((sched_job), struct drm_sched_job, queue_node)
>>>>    
>>>> -int drm_sched_policy = DRM_SCHED_POLICY_RR;
>>>> +int drm_sched_policy = DRM_SCHED_POLICY_FIFO;
>>>>    
>>>>    /**
>>>>     * DOC: sched_policy (int)
>>>>     * Used to override default entities scheduling policy in a run queue.
>>>>     */
>>>> -MODULE_PARM_DESC(sched_policy, "Specify schedule policy for entities on a runqueue, " __stringify(DRM_SCHED_POLICY_RR) " = Round Robin (default), " __stringify(DRM_SCHED_POLICY_FIFO) " = use FIFO.");
>>>> +MODULE_PARM_DESC(sched_policy, "Specify the scheduling policy for entities on a run-queue, " __stringify(DRM_SCHED_POLICY_RR) " = Round Robin, " __stringify(DRM_SCHED_POLICY_FIFO) " = FIFO (default).");
>>>>    module_param_named(sched_policy, drm_sched_policy, int, 0444);
>>>>    
>>>>    static __always_inline bool drm_sched_entity_compare_before(struct rb_node *a,
>>>>
>>>> base-commit: 16d2a3f2ad1d2b95bf9122c910c63b0efe74179d
>