linux-kernel - Re: [PATCH v4 0/3] riscv: optimized mem* functions

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Date:   Thu, 07 Oct 2021 18:26:44 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     mcroce@...ux.microsoft.com
CC:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, Atish Patra <Atish.Patra@....com>,
        kernel@...il.dk, akira.tsukamoto@...il.com, drew@...gleboard.org,
        bmeng.cn@...il.com, David.Laight@...lab.com, guoren@...nel.org,
        Christoph Hellwig <hch@....de>
Subject:     Re: [PATCH v4 0/3] riscv: optimized mem* functions

On Sun, 19 Sep 2021 12:21:01 PDT (-0700), mcroce@...ux.microsoft.com wrote:
> From: Matteo Croce <mcroce@...rosoft.com>
>
> Replace the assembly mem{cpy,move,set} with C equivalent.
>
> Try to access RAM with the largest bit width possible, but without
> doing unaligned accesses.
>
> A further improvement could be to use multiple read and writes as the
> assembly version was trying to do.
>
> Tested on a BeagleV Starlight with a SiFive U74 core, where the
> improvement is noticeable.
>
> v3 -> v4:
> - incorporate changes from proposed generic version:
>   https://lore.kernel.org/lkml/20210617152754.17960-1-mcroce@linux.microsoft.com/
>
> v2 -> v3:
> - alias mem* to __mem* and not viceversa
> - use __alias instead of a tail call
>
> v1 -> v2:
> - reduce the threshold from 64 to 16 bytes
> - fix KASAN build
> - optimize memset
>
> Matteo Croce (3):
>   riscv: optimized memcpy
>   riscv: optimized memmove
>   riscv: optimized memset
>
>  arch/riscv/include/asm/string.h |  18 ++--
>  arch/riscv/kernel/Makefile      |   1 -
>  arch/riscv/kernel/riscv_ksyms.c |  17 ----
>  arch/riscv/lib/Makefile         |   4 +-
>  arch/riscv/lib/memcpy.S         | 108 ----------------------
>  arch/riscv/lib/memmove.S        |  64 -------------
>  arch/riscv/lib/memset.S         | 113 -----------------------
>  arch/riscv/lib/string.c         | 154 ++++++++++++++++++++++++++++++++
>  8 files changed, 164 insertions(+), 315 deletions(-)
>  delete mode 100644 arch/riscv/kernel/riscv_ksyms.c
>  delete mode 100644 arch/riscv/lib/memcpy.S
>  delete mode 100644 arch/riscv/lib/memmove.S
>  delete mode 100644 arch/riscv/lib/memset.S
>  create mode 100644 arch/riscv/lib/string.c

Thanks.  These generally look good, but they're failing to build for me.  
I'm getting errors along the lines of

    arch/riscv/lib/string.c:89:7: error: inlining failed in call to ‘always_inline’ ‘memcpy’: function body can be overwritten at link time
       89 | void *memcpy(void *dest, const void *src, size_t count) __weak __alias(__memcpy);      |       ^~~~~~
    arch/riscv/lib/string.c:99:10: note: called from here
       99 |   return memcpy(dest, src, count);
          |          ^~~~~~~~~~~~~~~~~~~~~~~~

I'm still a bit behind on email so I'm going to keep going through 
patches, but if there's no v5 by the time I get back here then I'll take 
a look.