Ksawlii/kernel_samsung_a53x
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

lib/string: optimized memset

Browse source 
The generic memset is defined as a byte at time write.  This is always
safe, but it's slower than a 4 byte or even 8 byte write.

Write a generic memset which fills the data one byte at time until the
destination is aligned, then fills using the largest size allowed, and
finally fills the remaining data one byte at time.

On a RISC-V machine the speed goes from 140 Mb/s to 241 Mb/s, and this the
binary size increase according to bloat-o-meter:

Function     old     new   delta
memset        32     148    +116

Link: https://lkml.kernel.org/r/20210702123153.14093-4-mcroce@linux.microsoft.com
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Laight <David.Laight@aculab.com>
Cc: Drew Fustini <drew@beagleboard.org>
Cc: Emil Renner Berthing <kernel@esmil.dk>
Cc: Guo Ren <guoren@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nick Kossifidis <mick@ics.forth.gr>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jebaitedneko <Jebaitedneko@gmail.com>
Signed-off-by: celtare21 <celtare21@gmail.com>
This commit is contained in:
Matteo Croce 2021-07-16 19:26:42 +05:30 • committed by Ksawlii
parent 82413308e6
commit e4f231582a
1 changed files with 30 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

32
lib/string.c
View file

@ -796,10 +796,38 @@ EXPORT_SYMBOL(__sysfs_match_string);
*/
void *memset(void *s, int c, size_t count)
{
char *xs = s;
union types dest = { .as_u8 = s };
if (count >= MIN_THRESHOLD) {
unsigned long cu = (unsigned long)c;
/* Compose an ulong with 'c' repeated 4/8 times */
#ifdef CONFIG_ARCH_HAS_FAST_MULTIPLIER
cu *= 0x0101010101010101UL;
#else
cu |= cu << 8;
cu |= cu << 16;
/* Suppress warning on 32 bit machines */
cu |= (cu << 16) << 16;
#endif
if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) {
/*
* Fill the buffer one byte at time until
* the destination is word aligned.
*/
for (; count && dest.as_uptr & WORD_MASK; count--)
*dest.as_u8++ = c;
}
/* Copy using the largest size allowed */
for (; count >= BYTES_LONG; count -= BYTES_LONG)
*dest.as_ulong++ = cu;
}
/* copy the remainder */
while (count--)
*xs++ = c;
*dest.as_u8++ = c;
return s;
}
EXPORT_SYMBOL(memset);