Am 09.09.24 um 15:27 schrieb Tvrtko Ursulin:
On 09/09/2024 13:46, Philipp Stanner wrote:
On Mon, 2024-09-09 at 13:37 +0100, Tvrtko Ursulin wrote:
[SNIP]
That could also be a great opportunity for improving the lock
naming:
Well that comment made me laugh because I point out the same when
the
scheduler came out ~8years ago and nobody cared about it since
then.
But yeah completely agree :)
Maybe, but we need to keep in sight the fact some of these fixes may
be
good to backport. In which case re-naming exercises are best left to
follow.
My argument basically. It's good if fixes and other improvements are
separated, in general, unless there is a practical / good reason not
to.
Ah cool, I am happy to add follow up patches after the fixes.
+1
Also..
void drm_sched_rq_update_fifo(struct drm_sched_entity *entity,
ktime_t
ts)
{
/*
* Both locks need to be grabbed, one to protect from entity-
rq
change
* for entity from within concurrent
drm_sched_entity_select_rq
and the
* other to update the rb tree structure.
*/
spin_lock(&entity->rq_lock);
spin_lock(&entity->rq->lock);
.. I agree this is quite unredable and my initial reaction was a
similar
ugh. However.. What names would you guys suggest and for what to make
this better and not lessen the logic of naming each individually?
According to the documentation, drm_sched_rq.lock does not protect the
entire runque, but "@lock: to modify the entities list."
So I would keep drm_sched_entity.rq_lock as it is, because it indeed
protects the entire runqueue.
Agreed on entity->rq_lock.
I would just name that lock since it should be a protection of fields in
the drm_sched_entity structure.
That those fields are the rq and priority member should not necessary
have an influence on the name of the lock protecting it.
Only when we have multiple locks in the same structure then we need to
start giving them distinct names.
And drm_sched_rq.lock could be named "entities_lock" or
"entities_list_lock" or something. That's debatable, but it should be
something that highlights that this lock is not for locking the entire
runque as the one in the entity apparently is.
AFAICT it also protects rq->current_entity and rq->rb_tree_root in
which case it is a bit more tricky. Only rq->sched is outside its
scope. Hm. Maybe just re-arrange the struct to be like:
struct drm_sched_rq {
struct drm_gpu_scheduler *sched;
spinlock_t lock;
/* Following members are protected by the @lock: */
struct list_head entities;
struct drm_sched_entity *current_entity;
struct rb_root_cached rb_tree_root;
};
I have no ideas for better naming. But this would be inline with
Christian's suggestion for tidying the order in drm_sched_entity.
+1
Yeah I mean see the other structure we have in DRM and general Linux
kernel. The stuff that is static is usually grouped together since that
is good for cache locality and documentation at the same time.
I am also not sure what is the point of setting rq->current_entity in
drm_sched_rq_select_entity_fifo().
No idea either, Luben could answer that.
Christian.
Regards,
Tvrtko
Cheers,
P.
Regards,
Tvrtko
[...]
P.
Then audit the code if all users of rq and priority actually
hold the
correct locks while reading and writing them.
Regards,
Christian.
P.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>
Fixes: b37aced31eb0 ("drm/scheduler: implement a function
to
modify
sched list")
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: Luben Tuikov <ltuikov89@xxxxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx> # v5.7+
---
drivers/gpu/drm/scheduler/sched_entity.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/gpu/drm/scheduler/sched_entity.c
b/drivers/gpu/drm/scheduler/sched_entity.c
index 58c8161289fe..ae8be30472cd 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -133,8 +133,10 @@ void
drm_sched_entity_modify_sched(struct
drm_sched_entity *entity,
{
WARN_ON(!num_sched_list || !sched_list);
+ spin_lock(&entity->rq_lock);
entity->sched_list = sched_list;
entity->num_sched_list = num_sched_list;
+ spin_unlock(&entity->rq_lock);
}
EXPORT_SYMBOL(drm_sched_entity_modify_sched);
