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>,
Sven Schnelle <svens@linux.ibm.com>,
Russell King <linux@armlinux.org.uk>
Subject: Re: [PATCH v4 3/4] lib/find_bit: optimize find_next_bit() functions
Date: Thu, 15 Sep 2022 17:25:24 +0100 [thread overview]
Message-ID: <xhsmh4jx8bo5n.mognet@vschneid.remote.csb> (raw)
In-Reply-To: <20220915020730.852234-4-yury.norov@gmail.com>
On 14/09/22 19:07, Yury Norov wrote:
> Over the past couple years, the function _find_next_bit() was extended
> with parameters that modify its behavior to implement and- zero- and le-
> flavors. The parameters are passed at compile time, but current design
> prevents a compiler from optimizing out the conditionals.
>
> As find_next_bit() API grows, I expect that more parameters will be added.
> Current design would require more conditional code in _find_next_bit(),
> which would bloat the helper even more and make it barely readable.
>
> This patch replaces _find_next_bit() with a macro FIND_NEXT_BIT, and adds
> a set of wrappers, so that the compile-time optimizations become possible.
>
> The common logic is moved to the new macro, and all flavors may be
> generated by providing a FETCH macro parameter, like in this example:
>
> #define FIND_NEXT_BIT(FETCH, MUNGE, size, start) ...
>
> find_next_xornot_and_bit(addr1, addr2, addr3, size, start)
> {
> return FIND_NEXT_BIT(addr1[idx] ^ ~addr2[idx] & addr3[idx],
> /* nop */, size, start);
> }
>
> The FETCH may be of any complexity, as soon as it only refers the bitmap(s)
> and an iterator idx.
>
> MUNGE is here to support _le code generation for BE builds. May be
> empty.
>
> I ran find_bit_benchmark 16 times on top of 6.0-rc2 and 16 times on top
> of 6.0-rc2 + this series. The results for kvm/x86_64 are:
>
> v6.0-rc2 Optimized Difference Z-score
> Random dense bitmap ns ns ns %
> find_next_bit: 787735 670546 117189 14.9 3.97
> find_next_zero_bit: 777492 664208 113284 14.6 10.51
> find_last_bit: 830925 687573 143352 17.3 2.35
> find_first_bit: 3874366 3306635 567731 14.7 1.84
> find_first_and_bit: 40677125 37739887 2937238 7.2 1.36
> find_next_and_bit: 347865 304456 43409 12.5 1.35
>
> Random sparse bitmap
> find_next_bit: 19816 14021 5795 29.2 6.10
> find_next_zero_bit: 1318901 1223794 95107 7.2 1.41
> find_last_bit: 14573 13514 1059 7.3 6.92
> find_first_bit: 1313321 1249024 64297 4.9 1.53
> find_first_and_bit: 8921 8098 823 9.2 4.56
> find_next_and_bit: 9796 7176 2620 26.7 5.39
>
> Where the statistics is significant (z-score > 3), the improvement
> is ~15%.
>
> According to the bloat-o-meter, the Image size is 10-11K less:
>
> x86_64/defconfig:
> add/remove: 32/14 grow/shrink: 61/782 up/down: 6344/-16521 (-10177)
>
> arm64/defconfig:
> add/remove: 3/2 grow/shrink: 50/714 up/down: 608/-11556 (-10948)
>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
next prev parent reply other threads:[~2022-09-15 16:25 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-15 2:07 [PATCH v4 0/4] lib: optimize find_bit() functions Yury Norov
2022-09-15 2:07 ` [PATCH v4 1/4] lib/find_bit: introduce FIND_FIRST_BIT() macro Yury Norov
2022-09-15 2:07 ` [PATCH v4 2/4] lib/find_bit: create find_first_zero_bit_le() Yury Norov
2022-09-19 13:45 ` Andy Shevchenko
2022-09-15 2:07 ` [PATCH v4 3/4] lib/find_bit: optimize find_next_bit() functions Yury Norov
2022-09-15 16:25 ` Valentin Schneider [this message]
2022-09-19 13:45 ` Andy Shevchenko
2022-09-19 15:23 ` Linus Torvalds
2022-09-20 11:59 ` Andy Shevchenko
2022-09-20 1:41 ` Yury Norov
2022-09-15 2:07 ` [PATCH v4 4/4] tools: sync find_bit() implementation Yury Norov
2022-09-21 15:40 ` [PATCH v4 0/4] lib: optimize find_bit() functions Yury Norov
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