From 41ed7804350839608308fed0225894fdab8b71fd Mon Sep 17 00:00:00 2001 From: Kuan-Wei Chiu Date: Tue, 28 May 2024 04:30:10 +0800 Subject: [PATCH] lib/sort: optimize heapsort for handling final 2 or 3 elements After building the heap, the code continuously pops two elements from the heap until only 2 or 3 elements remain, at which point it switches back to a regular heapsort with one element popped at a time. However, to handle the final 2 or 3 elements, an additional else-if statement in the while loop was introduced, potentially increasing branch misses. Moreover, when there are only 2 or 3 elements left, continuing with regular heapify operations is unnecessary as these cases are simple enough to be handled with a single comparison and 1 or 2 swaps outside the while loop. Eliminating the additional else-if statement and directly managing cases involving 2 or 3 elements outside the loop reduces unnecessary conditional branches resulting from the numerous loops and conditionals in heapify. This optimization maintains consistent numbers of comparisons and swaps for arrays with even lengths while reducing swaps and comparisons for arrays with odd lengths from 2.5 swaps and 1 comparison to 1.5 swaps and 1 comparison. Link: https://lkml.kernel.org/r/20240527203011.1644280-4-visitorckw@gmail.com Signed-off-by: Kuan-Wei Chiu Cc: Ching-Chun (Jim) Huang Signed-off-by: Andrew Morton --- lib/sort.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/lib/sort.c b/lib/sort.c index b918ae15302d..048b7a6ef967 100644 --- a/lib/sort.c +++ b/lib/sort.c @@ -250,10 +250,7 @@ void sort_r(void *base, size_t num, size_t size, a = size << shift; n -= size; do_swap(base + a, base + n, size, swap_func, priv); - } else if (n > size) { /* Sorting: Extract root */ - n -= size; - do_swap(base, base + n, size, swap_func, priv); - } else { /* Sort complete */ + } else { /* Sort complete */ break; } @@ -283,6 +280,11 @@ void sort_r(void *base, size_t num, size_t size, do_swap(base + b, base + c, size, swap_func, priv); } } + + n -= size; + do_swap(base, base + n, size, swap_func, priv); + if (n == size * 2 && do_cmp(base, base + size, cmp_func, priv) > 0) + do_swap(base, base + size, size, swap_func, priv); } EXPORT_SYMBOL(sort_r);