| Message ID | 20240408174716.751069-1-visitorckw@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | d034d02de882d0ac600806724f9ffeb52de11e2e |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next,v2] net: sched: cake: Optimize the number of function calls and branches in heap construction | expand |
Kuan-Wei Chiu <visitorckw@gmail.com> writes: > 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> Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Hello: This patch was applied to netdev/net-next.git (main) by Jakub Kicinski <kuba@kernel.org>: On Tue, 9 Apr 2024 01:47:16 +0800 you wrote: > 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. > > [...] Here is the summary with links: - [net-next,v2] net: sched: cake: Optimize the number of function calls and branches in heap construction https://git.kernel.org/netdev/net-next/c/d034d02de882 You are awesome, thank you!
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;
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(-)