From: Pavel Machek <pavel@ucw.cz>
To: Yu-Jen Chang <arthurchang09@gmail.com>
Cc: andy@kernel.org, akinobu.mita@gmail.com, jserv@ccns.ncku.edu.tw,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/2] Optimize memchr()
Date: Fri, 12 Aug 2022 21:06:31 +0200 [thread overview]
Message-ID: <20220812190631.GA1347@bug> (raw)
In-Reply-To: <20220710142822.52539-1-arthurchang09@gmail.com>
Hi!
> This patche series optimized "memchr()" and add a macro for
> "memchr_inv()" so that both funtions can use it to generate bit mask.
>
> The original implementaion of "memchr()" is based on byte-wise comparison,
> which do not fully use 64-bit or 32-bit register in CPU. We implement a
> word-wise comparison so that at least 4 bytes can be compared at the same
> time. The optimized "memchr()" is nearly 4x faster than the original one
> for long strings. In Linux Kernel, we find that the length of the string
Well... how much slower is it for short strings?
> searched by "memchr()" is up to 512 bytes in drivers/misc/lkdtm/heap.c.
> In our test, the optimized version is about 20% faster if the target
> character is at the end of the string when going through a 512-byte
> string.
"What is the average length passed to memchr" would be more useful question.
Best regards,
Pavel
next prev parent reply other threads:[~2022-08-12 19:06 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-10 14:28 [PATCH 0/2] Optimize memchr() Yu-Jen Chang
2022-07-10 14:28 ` [PATCH 1/2] lib/string.c: Add a macro for memchr_inv() Yu-Jen Chang
2022-07-10 14:28 ` [PATCH 2/2] lib/string.c: Optimize memchr() Yu-Jen Chang
2022-07-10 15:16 ` Joe Perches
2022-07-11 14:50 ` Yu-Jen Chang
2022-07-10 16:58 ` kernel test robot
2022-07-10 20:01 ` Andrey Semashev
2022-07-11 14:52 ` Yu-Jen Chang
2022-07-11 15:00 ` Andrey Semashev
2022-07-11 15:03 ` Andy Shevchenko
2022-07-12 14:58 ` Yu-Jen Chang
2022-07-12 15:08 ` Andy Shevchenko
2022-07-13 9:39 ` David Laight
2022-07-13 9:49 ` Andrey Semashev
2022-07-13 10:02 ` Andrey Semashev
2022-07-13 10:24 ` David Laight
2022-07-22 16:08 ` Yu-Jen Chang
[not found] ` <CAHp75Vfy6wYqzT-T9aEjVEAQCZ_k=0qN8S8OwG3knbrC-oOkMQ@mail.gmail.com>
2022-07-29 15:42 ` Yu-Jen Chang
2022-07-13 9:57 ` Andrey Semashev
2022-07-21 5:06 ` kernel test robot
2022-08-12 19:06 ` Pavel Machek [this message]
2022-08-15 10:59 ` [PATCH 0/2] " David Laight
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