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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Fri, 25 Jun 2021 10:45:21 -0700
Message-ID: <CAKwvOd=rzoCFtUPrB+Hh8ZneGJwKc_2jW=QN6apb4T033r+kYg@mail.gmail.com>
Subject: Re: [PATCH 0/3] lib/string: optimized mem* functions
To:     Matteo Croce <mcroce@linux.microsoft.com>
Cc:     linux-kernel@vger.kernel.org, Nick Kossifidis <mick@ics.forth.gr>,
        Guo Ren <guoren@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        David Laight <David.Laight@aculab.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Emil Renner Berthing <kernel@esmil.dk>,
        Drew Fustini <drew@beagleboard.org>,
        linux-arch@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-riscv@lists.infradead.org
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On Thu, Jun 24, 2021 at 6:02 PM Matteo Croce <mcroce@linux.microsoft.com> wrote:
>
> From: Matteo Croce <mcroce@microsoft.com>
>
> Rewrite the generic mem{cpy,move,set} so that memory is accessed with
> the widest size possible, but without doing unaligned accesses.
>
> This was originally posted as C string functions for RISC-V[1], but as
> there was no specific RISC-V code, it was proposed for the generic
> lib/string.c implementation.
>
> Tested on RISC-V and on x86_64 by undefining __HAVE_ARCH_MEM{CPY,SET,MOVE}
> and HAVE_EFFICIENT_UNALIGNED_ACCESS.
>
> Further testing on big endian machines will be appreciated, as I don't
> have such hardware at the moment.

Hi Matteo,
Neat patches.  Do you have you any benchmark data showing the claimed
improvements? Is it worthwhile to define these only when
CC_OPTIMIZE_FOR_PERFORMANCE/CC_OPTIMIZE_FOR_PERFORMANCE_O3 are
defined, not CC_OPTIMIZE_FOR_SIZE? I'd be curious to know the delta in
ST_SIZE of these functions otherwise.

For big endian, you ought to be able to boot test in QEMU.  I think
you'd find out pretty quickly if any of the above had issues.
(Enabling KASAN is probably also a good idea for a test, too). Check
out
https://github.com/ClangBuiltLinux/boot-utils
for ready made images and scripts for launching various architectures
and endiannesses.

>
> [1] https://lore.kernel.org/linux-riscv/20210617152754.17960-1-mcroce@linux.microsoft.com/
>
> Matteo Croce (3):
>   lib/string: optimized memcpy
>   lib/string: optimized memmove
>   lib/string: optimized memset
>
>  lib/string.c | 129 ++++++++++++++++++++++++++++++++++++++++++++-------
>  1 file changed, 112 insertions(+), 17 deletions(-)
>
> --
> 2.31.1
>


--
Thanks,
~Nick Desaulniers