The patch titled
Subject: lib/string: optimized memset
has been added to the -mm tree. Its filename is
lib-string-optimized-memset.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/lib-string-optimized-memset.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/lib-string-optimized-memset.patch
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The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
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);
_
Patches currently in -mm which might be from mcroce@xxxxxxxxxxxxx are
revert-mm-page_alloc-make-should_fail_alloc_page-static.patch
lib-string-optimized-memcpy.patch
lib-string-optimized-memmove.patch
lib-string-optimized-memset.patch
