From: Christoph Hellwig <hch@infradead.org>
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 1/3] riscv: optimized memcpy
Date: Mon, 21 Jun 2021 15:26:31 +0100 [thread overview]
Message-ID: <YNChl0tkofSGzvIX@infradead.org> (raw)
In-Reply-To: <20210617152754.17960-2-mcroce@linux.microsoft.com>
On Thu, Jun 17, 2021 at 05:27:52PM +0200, Matteo Croce wrote:
> +extern void *memcpy(void *dest, const void *src, size_t count);
> +extern void *__memcpy(void *dest, const void *src, size_t count);
No need for externs.
> +++ b/arch/riscv/lib/string.c
Nothing in her looks RISC-V specific. Why doesn't this go into lib/ so
that other architectures can use it as well.
> +#include <linux/module.h>
I think you only need export.h.
> +void *__memcpy(void *dest, const void *src, size_t count)
> +{
> + const int bytes_long = BITS_PER_LONG / 8;
> +#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> + const int mask = bytes_long - 1;
> + const int distance = (src - dest) & mask;
> +#endif
> + union const_types s = { .u8 = src };
> + union types d = { .u8 = dest };
> +
> +#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> + if (count < MIN_THRESHOLD)
Using IS_ENABLED we can avoid a lot of the mess in this
function.
int distance = 0;
if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) {
if (count < MIN_THRESHOLD)
goto copy_remainder;
/* copy a byte at time until destination is aligned */
for (; count && d.uptr & mask; count--)
*d.u8++ = *s.u8++;
distance = (src - dest) & mask;
}
if (distance) {
...
> + /* 32/64 bit wide copy from s to d.
> + * d is aligned now but s is not, so read s alignment wise,
> + * and do proper shift to get the right value.
> + * Works only on Little Endian machines.
> + */
Normal kernel comment style always start with a:
/*
> + for (next = s.ulong[0]; count >= bytes_long + mask; count -= bytes_long) {
Please avoid the pointlessly overlong line. And (just as a matter of
personal preference) I find for loop that don't actually use a single
iterator rather confusing. Wjy not simply:
next = s.ulong[0];
while (count >= bytes_long + mask) {
...
count -= bytes_long;
}
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next prev parent reply other threads:[~2021-06-21 14:27 UTC|newest]
Thread overview: 23+ 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 ` [PATCH v3 1/3] riscv: optimized memcpy Matteo Croce
2021-06-18 14:06 ` kernel test robot
2021-06-21 14:26 ` Christoph Hellwig [this message]
2021-06-22 8:19 ` David Laight
2021-06-22 22:53 ` Matteo Croce
2021-06-22 22:00 ` Matteo Croce
2021-06-22 0:14 ` Nick Kossifidis
2021-06-22 23:35 ` Matteo Croce
2021-06-23 9:48 ` Nick Kossifidis
2021-06-17 15:27 ` [PATCH v3 2/3] riscv: optimized memmove Matteo Croce
2021-06-21 14:28 ` Christoph Hellwig
2021-06-22 0:46 ` Nick Kossifidis
2021-06-30 4:40 ` kernel test robot
2021-06-17 15:27 ` [PATCH v3 3/3] riscv: optimized memset Matteo Croce
2021-06-21 14:32 ` Christoph Hellwig
2021-06-22 1:07 ` Nick Kossifidis
2021-06-22 8:38 ` David Laight
2021-06-23 1:14 ` Matteo Croce
2021-06-23 9:05 ` David Laight
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 2:39 ` Guo Ren
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