From d034d02de882d0ac600806724f9ffeb52de11e2e Mon Sep 17 00:00:00 2001 From: Kuan-Wei Chiu Date: Tue, 9 Apr 2024 01:47:16 +0800 Subject: [PATCH] net: sched: cake: Optimize the number of function calls and branches in heap construction MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Acked-by: Toke Høiland-Jørgensen Link: https://lore.kernel.org/r/20240408174716.751069-1-visitorckw@gmail.com Signed-off-by: Jakub Kicinski --- 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 edee926ccde8b..2eabc4dc5b79a 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; -- 2.30.2