From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Yury Norov <yury.norov@gmail.com>, linux-kernel@vger.kernel.org
Cc: 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>,
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: Re: [PATCH 04/13] lib: introduce BITS_{FIRST,LAST} macro
Date: Tue, 16 Mar 2021 09:35:35 +0100 [thread overview]
Message-ID: <8021faab-e592-9587-329b-817ae007b89a@rasmusvillemoes.dk> (raw)
In-Reply-To: <20210316015424.1999082-5-yury.norov@gmail.com>
On 16/03/2021 02.54, Yury Norov wrote:
> BITMAP_{LAST,FIRST}_WORD_MASK() in linux/bitmap.h duplicates the
> functionality of GENMASK(). The scope of BITMAP* macros is wider
> than just bitmaps. This patch defines 4 new macros: BITS_FIRST(),
> BITS_LAST(), BITS_FIRST_MASK() and BITS_LAST_MASK() in linux/bits.h
> on top of GENMASK() and replaces BITMAP_{LAST,FIRST}_WORD_MASK()
> to avoid duplication and increase the scope of the macros.
>
> This change doesn't affect code generation. On ARM64:
> scripts/bloat-o-meter vmlinux.before vmlinux
> add/remove: 1/2 grow/shrink: 2/0 up/down: 17/-16 (1)
> Function old new delta
> ethtool_get_drvinfo 900 908 +8
> e843419@0cf2_0001309d_7f0 - 8 +8
> vermagic 48 49 +1
> e843419@0d45_000138bb_f68 8 - -8
> e843419@0cc9_00012bce_198c 8 - -8
[what on earth are those weird symbols?]
> diff --git a/include/linux/bits.h b/include/linux/bits.h
> index 7f475d59a097..8c191c29506e 100644
> --- a/include/linux/bits.h
> +++ b/include/linux/bits.h
> @@ -37,6 +37,12 @@
> #define GENMASK(h, l) \
> (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
>
> +#define BITS_FIRST(nr) GENMASK((nr), 0)
> +#define BITS_LAST(nr) GENMASK(BITS_PER_LONG - 1, (nr))
> +
> +#define BITS_FIRST_MASK(nr) BITS_FIRST((nr) % BITS_PER_LONG)
> +#define BITS_LAST_MASK(nr) BITS_LAST((nr) % BITS_PER_LONG)
I don't think it's a good idea to propagate the unusual closed-range
semantics of GENMASK to those wrappers. Almost all C and kernel code
uses the 'inclusive lower bound, exclusive upper bound', and I'd expect
BITS_FIRST(5) to result in a word with five bits set, not six. So I
think these changes as-is make the code much harder to read and understand.
Regardless, please add some comments on the valid input ranges to the
macros, whether that ends up being 0 <= nr < BITS_PER_LONG or 0 < nr <=
BITS_PER_LONG or whatnot.
It would also be much easier to review if you just redefined the
BITMAP_LAST_WORD_MASK macros etc. in terms of these new things, so you
wouldn't have to do a lot of mechanical changes at the same time as
introducing the new ones - especially when those mechanical changes
involve adding a "minus 1" everywhere.
Rasmus
next prev parent reply other threads:[~2021-03-16 8:36 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 1:54 [PATCH v4 00/13] lib/find_bit: fast path for small bitmaps Yury Norov
2021-03-16 1:54 ` [PATCH 01/13] tools: disable -Wno-type-limits Yury Norov
2021-03-16 8:17 ` Rasmus Villemoes
2021-03-16 11:39 ` Andy Shevchenko
2021-03-16 1:54 ` [PATCH 02/13] tools: bitmap: sync function declarations with the kernel Yury Norov
2021-03-16 8:18 ` Rasmus Villemoes
2021-03-16 1:54 ` [PATCH 03/13] arch: rearrange headers inclusion order in asm/bitops for m68k and sh Yury Norov
2021-03-16 1:54 ` [PATCH 04/13] lib: introduce BITS_{FIRST,LAST} macro Yury Norov
2021-03-16 8:35 ` Rasmus Villemoes [this message]
2021-03-16 11:42 ` Andy Shevchenko
2021-03-17 5:40 ` Yury Norov
2021-03-17 19:58 ` Rasmus Villemoes
2021-03-17 23:33 ` Yury Norov
2021-03-16 1:54 ` [PATCH 05/13] tools: sync BITS_MASK macros with the kernel Yury Norov
2021-03-16 1:54 ` [PATCH 06/13] lib: extend the scope of small_const_nbits() macro Yury Norov
2021-03-16 8:56 ` Rasmus Villemoes
2021-03-17 4:53 ` Yury Norov
2021-03-16 1:54 ` [PATCH 07/13] tools: sync small_const_nbits() macro with the kernel Yury Norov
2021-03-16 1:54 ` [PATCH 08/13] lib: inline _find_next_bit() wrappers Yury Norov
2021-03-16 1:54 ` [PATCH 09/13] tools: sync find_next_bit implementation Yury Norov
2021-03-16 1:54 ` [PATCH 10/13] lib: add fast path for find_next_*_bit() Yury Norov
2021-03-16 1:54 ` [PATCH 11/13] lib: add fast path for find_first_*_bit() and find_last_bit() Yury Norov
2021-04-06 16:03 ` Guenter Roeck
2021-04-06 18:15 ` Yury Norov
2021-03-16 1:54 ` [PATCH 12/13] tools: sync lib/find_bit implementation Yury Norov
2021-03-16 1:54 ` [PATCH 13/13] MAINTAINERS: Add entry for the bitmap API Yury Norov
2021-03-16 11:45 ` Andy Shevchenko
2021-03-17 4:47 ` Yury Norov
2021-03-17 4:57 ` Joe Perches
2021-03-17 6:40 ` Lukas Bulwahn
2021-03-17 19:29 ` Yury Norov
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