From: Kuan-Wei Chiu <visitorckw@gmail.com>
To: toke@toke.dk
Cc: jhs@mojatatu.com, xiyou.wangcong@gmail.com, jiri@resnulli.us,
davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
pabeni@redhat.com, jserv@ccns.ncku.edu.tw,
cake@lists.bufferbloat.net, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
Kuan-Wei Chiu <visitorckw@gmail.com>
Subject: [PATCH net-next v2] net: sched: cake: Optimize the number of function calls and branches in heap construction
Date: Tue, 9 Apr 2024 01:47:16 +0800 [thread overview]
Message-ID: <20240408174716.751069-1-visitorckw@gmail.com> (raw)
When constructing a heap, heapify operations are required on all
non-leaf nodes. Thus, determining the index of the first non-leaf node
is crucial. In a heap, the left child's index of node i is 2 * i + 1
and the right child's index is 2 * i + 2. Node CAKE_MAX_TINS *
CAKE_QUEUES / 2 has its left and right children at indexes
CAKE_MAX_TINS * CAKE_QUEUES + 1 and CAKE_MAX_TINS * CAKE_QUEUES + 2,
respectively, which are beyond the heap's range, indicating it as a
leaf node. Conversely, node CAKE_MAX_TINS * CAKE_QUEUES / 2 - 1 has a
left child at index CAKE_MAX_TINS * CAKE_QUEUES - 1, confirming its
non-leaf status. The loop should start from it since it's not a leaf
node.
By starting the loop from CAKE_MAX_TINS * CAKE_QUEUES / 2 - 1, we
minimize function calls and branch condition evaluations. This
adjustment theoretically reduces two function calls (one for
cake_heapify() and another for cake_heap_get_backlog()) and five branch
evaluations (one for iterating all non-leaf nodes, one within
cake_heapify()'s while loop, and three more within the while loop
with if conditions).
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
net/sched/sch_cake.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
index edee926ccde8..2eabc4dc5b79 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -1512,7 +1512,7 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
if (!q->overflow_timeout) {
int i;
/* Build fresh max-heap */
- for (i = CAKE_MAX_TINS * CAKE_QUEUES / 2; i >= 0; i--)
+ for (i = CAKE_MAX_TINS * CAKE_QUEUES / 2 - 1; i >= 0; i--)
cake_heapify(q, i);
}
q->overflow_timeout = 65535;
--
2.34.1
next reply other threads:[~2024-04-08 17:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-08 17:47 Kuan-Wei Chiu [this message]
2024-04-09 9:45 ` [PATCH net-next v2] net: sched: cake: Optimize the number of function calls and branches in heap construction Toke Høiland-Jørgensen
2024-04-10 0:40 ` patchwork-bot+netdevbpf
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