From: Valentin Schneider <vschneid@redhat.com>
To: Yury Norov <yury.norov@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org
Cc: Yury Norov <yury.norov@gmail.com>,
Alexey Klimov <klimov.linux@gmail.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Andy Whitcroft <apw@canonical.com>,
Catalin Marinas <catalin.marinas@arm.com>,
David Laight <David.Laight@ACULAB.COM>,
Dennis Zhou <dennis@kernel.org>,
Guenter Roeck <linux@roeck-us.net>,
Kees Cook <keescook@chromium.org>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
Russell King <linux@armlinux.org.uk>
Subject: Re: [PATCH v3 3/4] lib/find_bit: optimize find_next_bit() functions
Date: Wed, 07 Sep 2022 17:27:08 +0100 [thread overview]
Message-ID: <xhsmhfsh3b15v.mognet@vschneid.remote.csb> (raw)
In-Reply-To: <20220827175807.4017673-4-yury.norov@gmail.com>
On 27/08/22 10:58, Yury Norov wrote:
> +#define FIND_NEXT_BIT(FETCH, MUNGE, size, start) \
> +({ \
> + unsigned long mask, idx, tmp, sz = (size), __start = (start); \
> + \
> + if (unlikely(__start >= sz)) \
> + goto out; \
> + \
> + mask = MUNGE(BITMAP_FIRST_WORD_MASK(__start)); \
> + idx = __start / BITS_PER_LONG; \
> + \
> + for (tmp = (FETCH) & mask; !tmp; tmp = (FETCH)) { \
> + if (idx > sz / BITS_PER_LONG) \
Does that want to be
if (idx + 1 >= sz / BITS_PER_LONG)
?
Consider this as used in _find_next_bit() for an all-zero 128-bit wide
bitmap (two ULL's), providing the memory contiguous to the bitmap is also
zero then this will only stop at idx=3, so that's fetching two ULLs too
far.
> + goto out; \
> + idx++; \
> + } \
> + \
> + sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(tmp)), sz); \
> +out: \
> + sz; \
> +})
next prev parent reply other threads:[~2022-09-07 16:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-27 17:58 [PATCH v3 0/4] lib: optimize find_bit() functions Yury Norov
2022-08-27 17:58 ` [PATCH v3 1/4] lib/find_bit: introduce FIND_FIRST_BIT() macro Yury Norov
2022-09-07 16:27 ` Valentin Schneider
2022-08-27 17:58 ` [PATCH v3 2/4] lib/find_bit: create find_first_zero_bit_le() Yury Norov
2022-09-07 16:27 ` Valentin Schneider
2022-08-27 17:58 ` [PATCH v3 3/4] lib/find_bit: optimize find_next_bit() functions Yury Norov
2022-09-07 16:27 ` Valentin Schneider [this message]
2022-09-07 16:57 ` Yury Norov
2022-09-09 12:24 ` Sven Schnelle
2022-09-09 14:47 ` Yury Norov
2022-09-09 17:03 ` Andy Shevchenko
2022-08-27 17:58 ` [PATCH v3 4/4] tools: sync find_bit() implementation Yury Norov
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