linux-kernel - [PATCH] lib: Avoid redundant sizeof checking in __bitmap

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Date:   Tue, 14 Nov 2017 12:57:31 +0600
From:   Rakib Mullick <rakib.mullick@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Yury Norov <ynorov@...iumnetworks.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Subject: [PATCH]  lib: Avoid redundant sizeof checking in __bitmap_weight() calculation.

Currently, during __bitmap_weight() calculation hweight_long() is used.
Inside a hweight_long() a check has been made to figure out whether a
hweight32() or hweight64() version to use.

However, it's unnecessary to do it in case of __bitmap_weight() calculation
inside the loop. We can detect whether to use hweight32() or hweight64()
upfront and call respective function directly. It also reduces the
vmlinux size.

    Before the patch:
   text	   data	    bss	    dec	    hex	filename
12901332	7798930	14541816	35242078	219c05e	vmlinux

    After the patch:
   text	   data	    bss	    dec	    hex	filename
12901331	7798930	14541816	35242077	219c05d	vmlinux

Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Matthew Wilcox <mawilcox@...rosoft.com>
Cc: Yury Norov <ynorov@...iumnetworks.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
 
---
Patch was created against torvald's tree (commit 43ff2f4db9d0f764).

 lib/bitmap.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index d8f0c09..552096f 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -241,10 +241,15 @@ EXPORT_SYMBOL(__bitmap_subset);
 int __bitmap_weight(const unsigned long *bitmap, unsigned int bits)
 {
 	unsigned int k, lim = bits/BITS_PER_LONG;
-	int w = 0;
-
-	for (k = 0; k < lim; k++)
-		w += hweight_long(bitmap[k]);
+	int w = 0, is32 = sizeof(bitmap[0]) ? 1 : 0;
+
+	if (is32) {
+		for (k = 0; k < lim; k++)
+			w += hweight32(bitmap[k]);
+	} else {
+		for (k = 0; k < lim; k++)
+			w += hweight64(bitmap[k]);
+	}
 
 	if (bits % BITS_PER_LONG)
 		w += hweight_long(bitmap[k] & BITMAP_LAST_WORD_MASK(bits));
-- 
2.9.3