net: dql: Optimize stall information population

When Dynamic Queue Limit (DQL) is set, it always populate stall
information through dql_queue_stall().  However, this information is
only necessary if a stall threshold is set, stored in struct
dql->stall_thrs.

dql_queue_stall() is cheap, but not free, since it does have memory
barriers and so forth.

Do not call dql_queue_stall() if there is no stall threshold set, and
save some CPU cycles.

Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://lore.kernel.org/r/20240411192241.2498631-4-leitao@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/linux/dynamic_queue_limits.h b/include/linux/dynamic_queue_limits.h
index 9980df0b7247278a8eb4d592286259e8fe8059c8..869afb800ea1f329390f00f913a75f2ed86fe239 100644 (file)
--- a/include/linux/dynamic_queue_limits.h
+++ b/include/linux/dynamic_queue_limits.h
@@ -137,7 +137,9 @@ static inline void dql_queued(struct dql *dql, unsigned int count)
 
        dql->num_queued += count;
 
-       dql_queue_stall(dql);
+       /* Only populate stall information if the threshold is set */
+       if (READ_ONCE(dql->stall_thrs))
+               dql_queue_stall(dql);
 }
 
 /* Returns how many objects can be queued, < 0 indicates over limit. */