linux-kernel - [PATCH] lib: micro-optimization for __bitmap

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Message-Id: <20180411145914.6011-1-ynorov@caviumnetworks.com>
Date:   Wed, 11 Apr 2018 17:59:14 +0300
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Cc:     Yury Norov <ynorov@...iumnetworks.com>
Subject: [PATCH] lib: micro-optimization for __bitmap_complement()

Use BITS_TO_LONGS() macro to avoid calculation of reminder
(bits % BITS_PER_LONG) On ARM64 it saves 5 instruction for function -
16 before and 11 after.

Signed-off-by: Yury Norov <ynorov@...iumnetworks.com>
---
 lib/bitmap.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index c82c61b66e16..7adc10074cff 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -62,12 +62,9 @@ EXPORT_SYMBOL(__bitmap_equal);
 
 void __bitmap_complement(unsigned long *dst, const unsigned long *src, unsigned int bits)
 {
-	unsigned int k, lim = bits/BITS_PER_LONG;
+	unsigned int k, lim = BITS_TO_LONGS(bits);
 	for (k = 0; k < lim; ++k)
 		dst[k] = ~src[k];
-
-	if (bits % BITS_PER_LONG)
-		dst[k] = ~src[k];
 }
 EXPORT_SYMBOL(__bitmap_complement);
 
-- 
2.14.1