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 <[email protected]>
---
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
Kuan-Wei Chiu <[email protected]> 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 <[email protected]>
Acked-by: Toke Høiland-Jørgensen <[email protected]>
Hello:
This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <[email protected]>:
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!
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