From: Matteo Croce <mcroce@xxxxxxxxxxxxx> Subject: lib/string: optimized memset 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@xxxxxxxxxxxxxxxxxxx Signed-off-by: Matteo Croce <mcroce@xxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: David Laight <David.Laight@xxxxxxxxxx> Cc: Drew Fustini <drew@xxxxxxxxxxxxxxx> Cc: Emil Renner Berthing <kernel@xxxxxxxx> Cc: Guo Ren <guoren@xxxxxxxxxx> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Nick Kossifidis <mick@xxxxxxxxxxxx> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/string.c | 32 ++++++++++++++++++++++++++++++-- 1 file changed, 30 insertions(+), 2 deletions(-) --- a/lib/string.c~lib-string-optimized-memset +++ a/lib/string.c @@ -810,10 +810,38 @@ 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); _
