From: Nick Kossifidis <mick@ics.forth.gr> To: Matteo Croce <mcroce@linux.microsoft.com> Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Paul Walmsley <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, Atish Patra <atish.patra@wdc.com>, Emil Renner Berthing <kernel@esmil.dk>, Akira Tsukamoto <akira.tsukamoto@gmail.com>, Drew Fustini <drew@beagleboard.org>, Bin Meng <bmeng.cn@gmail.com>, David Laight <David.Laight@aculab.com>, Guo Ren <guoren@kernel.org> Subject: Re: [PATCH v3 2/3] riscv: optimized memmove Date: Tue, 22 Jun 2021 03:46:16 +0300 [thread overview] Message-ID: <3a71b234ec05b6ce842a3d6da552ba30@mailhost.ics.forth.gr> (raw) In-Reply-To: <20210617152754.17960-3-mcroce@linux.microsoft.com> Στις 2021-06-17 18:27, Matteo Croce έγραψε: > + > +/* > + * Simply check if the buffer overlaps an call memcpy() in case, > + * otherwise do a simple one byte at time backward copy. > + */ > +void *__memmove(void *dest, const void *src, size_t count) > +{ > + if (dest < src || src + count <= dest) > + return memcpy(dest, src, count); > + > + if (dest > src) { > + const char *s = src + count; > + char *tmp = dest + count; > + > + while (count--) > + *--tmp = *--s; > + } > + return dest; > +} > +EXPORT_SYMBOL(__memmove); > + Copying backwards byte-per-byte is suboptimal, I understand this is not a very common scenario but you could at least check if they are both word-aligned e.g. (((src + len) | (dst + len)) & mask), or missaligned by the same offset e.g. (((src + len) ^ (dst + len)) & mask) and still end up doing word-by-word copying. Ideally it would be great if you re-used the same technique you used for forwards copying on your memcpy. > +void *memmove(void *dest, const void *src, size_t count) __weak > __alias(__memmove); > +EXPORT_SYMBOL(memmove); As I mentioned on your memcpy patch, if you implement memmove, you can just alias memcpy to memmove and we won't have to worry about memcpy being used on overlapping regions.
WARNING: multiple messages have this Message-ID (diff)
From: Nick Kossifidis <mick@ics.forth.gr> To: Matteo Croce <mcroce@linux.microsoft.com> Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Paul Walmsley <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, Atish Patra <atish.patra@wdc.com>, Emil Renner Berthing <kernel@esmil.dk>, Akira Tsukamoto <akira.tsukamoto@gmail.com>, Drew Fustini <drew@beagleboard.org>, Bin Meng <bmeng.cn@gmail.com>, David Laight <David.Laight@aculab.com>, Guo Ren <guoren@kernel.org> Subject: Re: [PATCH v3 2/3] riscv: optimized memmove Date: Tue, 22 Jun 2021 03:46:16 +0300 [thread overview] Message-ID: <3a71b234ec05b6ce842a3d6da552ba30@mailhost.ics.forth.gr> (raw) In-Reply-To: <20210617152754.17960-3-mcroce@linux.microsoft.com> Στις 2021-06-17 18:27, Matteo Croce έγραψε: > + > +/* > + * Simply check if the buffer overlaps an call memcpy() in case, > + * otherwise do a simple one byte at time backward copy. > + */ > +void *__memmove(void *dest, const void *src, size_t count) > +{ > + if (dest < src || src + count <= dest) > + return memcpy(dest, src, count); > + > + if (dest > src) { > + const char *s = src + count; > + char *tmp = dest + count; > + > + while (count--) > + *--tmp = *--s; > + } > + return dest; > +} > +EXPORT_SYMBOL(__memmove); > + Copying backwards byte-per-byte is suboptimal, I understand this is not a very common scenario but you could at least check if they are both word-aligned e.g. (((src + len) | (dst + len)) & mask), or missaligned by the same offset e.g. (((src + len) ^ (dst + len)) & mask) and still end up doing word-by-word copying. Ideally it would be great if you re-used the same technique you used for forwards copying on your memcpy. > +void *memmove(void *dest, const void *src, size_t count) __weak > __alias(__memmove); > +EXPORT_SYMBOL(memmove); As I mentioned on your memcpy patch, if you implement memmove, you can just alias memcpy to memmove and we won't have to worry about memcpy being used on overlapping regions. _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv
next prev parent reply other threads:[~2021-06-22 0:46 UTC|newest] Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-17 15:27 [PATCH v3 0/3] riscv: optimized mem* functions Matteo Croce 2021-06-17 15:27 ` Matteo Croce 2021-06-17 15:27 ` [PATCH v3 1/3] riscv: optimized memcpy Matteo Croce 2021-06-17 15:27 ` Matteo Croce 2021-06-18 14:06 ` kernel test robot 2021-06-18 14:06 ` kernel test robot 2021-06-18 14:06 ` kernel test robot 2021-06-21 14:26 ` Christoph Hellwig 2021-06-21 14:26 ` Christoph Hellwig 2021-06-22 8:19 ` David Laight 2021-06-22 8:19 ` David Laight 2021-06-22 22:53 ` Matteo Croce 2021-06-22 22:53 ` Matteo Croce 2021-06-22 22:00 ` Matteo Croce 2021-06-22 22:00 ` Matteo Croce 2021-06-22 0:14 ` Nick Kossifidis 2021-06-22 0:14 ` Nick Kossifidis 2021-06-22 23:35 ` Matteo Croce 2021-06-22 23:35 ` Matteo Croce 2021-06-23 9:48 ` Nick Kossifidis 2021-06-23 9:48 ` Nick Kossifidis 2021-06-17 15:27 ` [PATCH v3 2/3] riscv: optimized memmove Matteo Croce 2021-06-17 15:27 ` Matteo Croce 2021-06-21 14:28 ` Christoph Hellwig 2021-06-21 14:28 ` Christoph Hellwig 2021-06-22 0:46 ` Nick Kossifidis [this message] 2021-06-22 0:46 ` Nick Kossifidis 2021-06-30 4:40 ` kernel test robot 2021-06-30 4:40 ` kernel test robot 2021-06-30 4:40 ` kernel test robot 2021-06-17 15:27 ` [PATCH v3 3/3] riscv: optimized memset Matteo Croce 2021-06-17 15:27 ` Matteo Croce 2021-06-21 14:32 ` Christoph Hellwig 2021-06-21 14:32 ` Christoph Hellwig 2021-06-22 1:07 ` Nick Kossifidis 2021-06-22 1:07 ` Nick Kossifidis 2021-06-22 8:38 ` David Laight 2021-06-22 8:38 ` David Laight 2021-06-23 1:14 ` Matteo Croce 2021-06-23 1:14 ` Matteo Croce 2021-06-23 9:05 ` David Laight 2021-06-23 9:05 ` David Laight 2021-06-23 0:08 ` Matteo Croce 2021-06-23 0:08 ` Matteo Croce 2021-06-22 1:09 ` [PATCH v3 0/3] riscv: optimized mem* functions Nick Kossifidis 2021-06-22 1:09 ` Nick Kossifidis 2021-06-22 2:39 ` Guo Ren 2021-06-22 2:39 ` Guo Ren
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