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From: Yury Norov <yury.norov@gmail.com>
To: linux-kernel@vger.kernel.org
Cc: Yury Norov <yury.norov@gmail.com>,
	linux-m68k@lists.linux-m68k.org, linux-arch@vger.kernel.org,
	linux-sh@vger.kernel.org, Alexey Klimov <aklimov@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Arnd Bergmann <arnd@arndb.de>, David Sterba <dsterba@suse.com>,
	Dennis Zhou <dennis@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Jianpeng Ma <jianpeng.ma@intel.com>,
	Joe Perches <joe@perches.com>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Rich Felker <dalias@libc.org>,
	Stefano Brivio <sbrivio@redhat.com>,
	Wei Yang <richard.weiyang@linux.alibaba.com>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: [PATCH 05/12] lib: extend the scope of small_const_nbits() macro
Date: Sun, 21 Mar 2021 14:54:50 -0700	[thread overview]
Message-ID: <20210321215457.588554-6-yury.norov@gmail.com> (raw)
In-Reply-To: <20210321215457.588554-1-yury.norov@gmail.com>

find_bit would also benefit from small_const_nbits() optimizations.
The detailed comment is provided by Rasmus Villemoes.

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 include/asm-generic/bitsperlong.h | 12 ++++++++++++
 include/linux/bitmap.h            |  8 --------
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/asm-generic/bitsperlong.h b/include/asm-generic/bitsperlong.h
index 3905c1c93dc2..1023e2a4bd37 100644
--- a/include/asm-generic/bitsperlong.h
+++ b/include/asm-generic/bitsperlong.h
@@ -23,4 +23,16 @@
 #define BITS_PER_LONG_LONG 64
 #endif
 
+/*
+ * small_const_nbits(n) is true precisely when it is known at compile-time
+ * that BITMAP_SIZE(n) is 1, i.e. 1 <= n <= BITS_PER_LONG. This allows
+ * various bit/bitmap APIs to provide a fast inline implementation. Bitmaps
+ * of size 0 are very rare, and a compile-time-known-size 0 is most likely
+ * a sign of error. They will be handled correctly by the bit/bitmap APIs,
+ * but using the out-of-line functions, so that the inline implementations
+ * can unconditionally dereference the pointer(s).
+ */
+#define small_const_nbits(nbits) \
+	(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0)
+
 #endif /* __ASM_GENERIC_BITS_PER_LONG */
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 70a932470b2d..8c4adfa5cceb 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -222,14 +222,6 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf,
 #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1)))
 #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
 
-/*
- * The static inlines below do not handle constant nbits==0 correctly,
- * so make such users (should any ever turn up) call the out-of-line
- * versions.
- */
-#define small_const_nbits(nbits) \
-	(__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0)
-
 static inline void bitmap_zero(unsigned long *dst, unsigned int nbits)
 {
 	unsigned int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
-- 
2.25.1


  parent reply	other threads:[~2021-03-21 21:56 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-21 21:54 [PATCH v5 00/12] lib/find_bit: fast path for small bitmaps Yury Norov
2021-03-21 21:54 ` [PATCH 01/12] tools: disable -Wno-type-limits Yury Norov
2021-03-21 21:54 ` [PATCH 02/12] tools: bitmap: sync function declarations with the kernel Yury Norov
2021-03-21 21:54 ` [PATCH 03/12] tools: sync BITMAP_LAST_WORD_MASK() macro " Yury Norov
2021-03-21 21:54 ` [PATCH 04/12] arch: rearrange headers inclusion order in asm/bitops for m68k and sh Yury Norov
2021-03-21 21:54 ` Yury Norov [this message]
2021-03-21 21:54 ` [PATCH 06/12] tools: sync small_const_nbits() macro with the kernel Yury Norov
2021-03-22  8:34   ` Rasmus Villemoes
2021-03-24 19:49     ` Yury Norov
2021-03-21 21:54 ` [PATCH 07/12] lib: inline _find_next_bit() wrappers Yury Norov
2021-03-21 21:54 ` [PATCH 08/12] tools: sync find_next_bit implementation Yury Norov
2021-03-21 21:54 ` [PATCH 09/12] lib: add fast path for find_next_*_bit() Yury Norov
2021-03-21 21:54 ` [PATCH 10/12] lib: add fast path for find_first_*_bit() and find_last_bit() Yury Norov
2021-03-21 21:54 ` [PATCH 11/12] tools: sync lib/find_bit implementation Yury Norov
2021-03-21 21:54 ` [PATCH 12/12] MAINTAINERS: Add entry for the bitmap API Yury Norov
2021-04-01  0:31 [PATCH v6 00/12] lib/find_bit: fast path for small bitmaps Yury Norov
2021-04-01  0:31 ` [PATCH 05/12] lib: extend the scope of small_const_nbits() macro Yury Norov
2021-04-01  8:35   ` Andy Shevchenko

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