linux-kernel - Re: [PATCH v2 1/3] lib/string: optimized memcpy

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Message-ID: <0e0fa030-8995-b930-5e22-954349a0b82e@codethink.co.uk>
Date:   Fri, 2 Jul 2021 15:37:19 +0100
From:   Ben Dooks <ben.dooks@...ethink.co.uk>
To:     Matteo Croce <mcroce@...ux.microsoft.com>,
        linux-kernel@...r.kernel.org, Nick Kossifidis <mick@....forth.gr>,
        Guo Ren <guoren@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        David Laight <David.Laight@...lab.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Emil Renner Berthing <kernel@...il.dk>,
        Drew Fustini <drew@...gleboard.org>
Cc:     linux-arch@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] lib/string: optimized memcpy

On 02/07/2021 13:31, Matteo Croce wrote:
> From: Matteo Croce <mcroce@...rosoft.com>
> 
> Rewrite the generic memcpy() to copy a word at time, without generating
> unaligned accesses.
> 
> The procedure is made of three steps:
> First copy data one byte at time until the destination buffer is aligned
> to a long boundary.
> Then copy the data one long at time shifting the current and the next long
> to compose a long at every cycle.
> Finally, copy the remainder one byte at time.
> 
> This is the improvement on RISC-V:
> 
> original aligned:	 75 Mb/s
> original unaligned:	 75 Mb/s
> new aligned:		114 Mb/s
> new unaligned:		107 Mb/s
> 
> and this the binary size increase according to bloat-o-meter:
> 
> Function     old     new   delta
> memcpy        36     324    +288
> 
> 
> Signed-off-by: Matteo Croce <mcroce@...rosoft.com>
> ---
>   lib/string.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 77 insertions(+), 3 deletions(-)

Doesn't arch/riscv/lib/memcpy.S also exist for an architecture
optimised version? I would have thought the lib/string.c version
was not being used?


-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

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