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| author | Kuan-Wei Chiu <visitorckw@gmail.com> | 2024-04-08 20:47:16 +0300 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2024-04-10 03:30:14 +0300 |
| commit | d034d02de882d0ac600806724f9ffeb52de11e2e (patch) | |
| tree | 7458cca7041f150998731e2b66ea78c0d3b316f0 /net/sched | |
| parent | 545d95e5f1ba87db17534ee8c36409dd2ade848b (diff) | |
| download | linux-d034d02de882d0ac600806724f9ffeb52de11e2e.tar.xz | |
net: sched: cake: Optimize the number of function calls and branches in heap construction
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>
Link: https://lore.kernel.org/r/20240408174716.751069-1-visitorckw@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/sched')
| -rw-r--r-- | net/sched/sch_cake.c | 2 |
1 files changed, 1 insertions, 1 deletions
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; |