From: Petr Mladek <pmladek@suse.com>
To: Yury Norov <yury.norov@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
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Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: Re: [PATCH 11/17] find: micro-optimize for_each_{set,clear}_bit()
Date: Thu, 26 Aug 2021 15:57:13 +0200 [thread overview]
Message-ID: <YSeduU41Ef568xhS@alley> (raw)
In-Reply-To: <20210814211713.180533-12-yury.norov@gmail.com>
On Sat 2021-08-14 14:17:07, Yury Norov wrote:
> The macros iterate thru all set/clear bits in a bitmap. They search a
> first bit using find_first_bit(), and the rest bits using find_next_bit().
>
> Since find_next_bit() is called shortly after find_first_bit(), we can
> save few lines of I-cache by not using find_first_bit().
Is this only a speculation or does it fix a real performance problem?
The macro is used like:
for_each_set_bit(bit, addr, size) {
fn(bit);
}
IMHO, the micro-opimization does not help when fn() is non-trivial.
> --- a/include/linux/find.h
> +++ b/include/linux/find.h
> @@ -280,7 +280,7 @@ unsigned long find_next_bit_le(const void *addr, unsigned
> #endif
>
> #define for_each_set_bit(bit, addr, size) \
> - for ((bit) = find_first_bit((addr), (size)); \
> + for ((bit) = find_next_bit((addr), (size), 0); \
> (bit) < (size); \
> (bit) = find_next_bit((addr), (size), (bit) + 1))
>
It is not a big deal. I just think that the original code is slightly
more self-explaining.
Best Regards,
Petr
next prev parent reply other threads:[~2021-08-26 13:57 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-14 21:16 [PATCH RESEND 00/17] Resend bitmap patches Yury Norov
2021-08-14 21:16 ` [PATCH 01/17] bitops: protect find_first_{,zero}_bit properly Yury Norov
2021-08-14 21:16 ` [PATCH 02/17] bitops: move find_bit_*_le functions from le.h to find.h Yury Norov
2021-08-14 21:16 ` [PATCH 03/17] include: move find.h from asm_generic to linux Yury Norov
2021-08-14 21:17 ` [PATCH 04/17] arch: remove GENERIC_FIND_FIRST_BIT entirely Yury Norov
2021-08-14 21:17 ` [PATCH 05/17] lib: add find_first_and_bit() Yury Norov
2021-08-14 21:17 ` [PATCH 06/17] cpumask: use find_first_and_bit() Yury Norov
2021-08-14 21:17 ` [PATCH 07/17] all: replace find_next{,_zero}_bit with find_first{,_zero}_bit where appropriate Yury Norov
2021-08-14 21:17 ` [PATCH 08/17] tools: sync tools/bitmap with mother linux Yury Norov
2021-08-14 21:17 ` [PATCH 09/17] cpumask: replace cpumask_next_* with cpumask_first_* where appropriate Yury Norov
2021-08-14 21:17 ` [PATCH 10/17] include/linux: move for_each_bit() macros from bitops.h to find.h Yury Norov
2021-08-14 21:17 ` [PATCH 11/17] find: micro-optimize for_each_{set,clear}_bit() Yury Norov
2021-08-26 13:57 ` Petr Mladek [this message]
2021-08-26 21:09 ` Yury Norov
2021-08-30 12:12 ` Petr Mladek
2021-08-30 16:15 ` Yury Norov
2021-08-14 21:17 ` [PATCH 12/17] Replace for_each_*_bit_from() with for_each_*_bit() where appropriate Yury Norov
2021-08-14 21:17 ` [PATCH 13/17] tools: Rename bitmap_alloc() to bitmap_zalloc() Yury Norov
2021-08-14 21:17 ` [PATCH 14/17] mm/percpu: micro-optimize pcpu_is_populated() Yury Norov
2021-08-14 21:17 ` [PATCH 15/17] bitmap: unify find_bit operations Yury Norov
2021-08-14 21:17 ` [PATCH 16/17] lib: bitmap: add performance test for bitmap_print_to_pagebuf Yury Norov
2021-08-14 21:17 ` [PATCH 17/17] vsprintf: rework bitmap_list_string Yury Norov
2021-08-15 11:09 ` Andy Shevchenko
2021-08-17 16:35 ` Yury Norov
2021-08-26 14:15 ` Petr Mladek
2021-08-26 20:59 ` Yury Norov
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