linux-kernel - [PATCH net-next 3/3] net: dql: Optimize stall information population

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Date: Thu,  4 Apr 2024 07:59:32 -0700
From: Breno Leitao <leitao@...ian.org>
To: kuba@...nel.org,
	davem@...emloft.net,
	pabeni@...hat.com,
	edumazet@...gle.com
Cc: linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: [PATCH net-next 3/3] 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@...ian.org>
---
 include/linux/dynamic_queue_limits.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/dynamic_queue_limits.h b/include/linux/dynamic_queue_limits.h
index 9980df0b7247..869afb800ea1 100644
--- 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. */
-- 
2.43.0