linux-kernel - [PATCH] lib/sort: Optimize number of calls to comparison function

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Message-Id: <20231202163717.687578-1-visitorckw@gmail.com>
Date:   Sun,  3 Dec 2023 00:37:17 +0800
From:   Kuan-Wei Chiu <visitorckw@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, lkml@....org,
        Kuan-Wei Chiu <visitorckw@...il.com>
Subject: [PATCH] lib/sort: Optimize number of calls to comparison function

The current implementation continues the loop when the comparison
function returns a non-negative value, which includes the case when it
returns 0. However, in scenarios where the comparison function returns
0, further comparisons are unnecessary. By making this adjustment, we
can potentially reduce the number of comparisons by approximately 50%
in extreme cases where all elements in the array are equal, and the
array size is sufficiently large.

Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
---
 lib/sort.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/sort.c b/lib/sort.c
index b399bf10d675..1e98a62bb2f3 100644
--- a/lib/sort.c
+++ b/lib/sort.c
@@ -267,7 +267,7 @@ void sort_r(void *base, size_t num, size_t size,
 			b = c;

 		/* Now backtrack from "b" to the correct location for "a" */
-		while (b != a && do_cmp(base + a, base + b, cmp_func, priv) >= 0)
+		while (b != a && do_cmp(base + a, base + b, cmp_func, priv) > 0)
 			b = parent(b, lsbit, size);
 		c = b;			/* Where "a" belongs */
 		while (b != a) {	/* Shift it into place */
-- 
2.25.1