The patch titled
Subject: string: memchr_inv speed improvements
has been added to the -mm tree. Its filename is
string-memchr_inv-speed-improvements.patch
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From: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Subject: string: memchr_inv speed improvements
- Generate a 64-bit pattern more efficiently
memchr_inv needs to generate a 64-bit pattern filled with a target
character. The operation can be done by more efficient way.
- Don't call the slow check_bytes() if the memory area is 64-bit aligned
memchr_inv compares contiguous 64-bit words with the 64-bit pattern as
much as possible. The outside of the region is checked by check_bytes()
that scans for each byte. Unfortunately, the first 64-bit word is
unexpectedly scanned by check_bytes() even if the memory area is aligned
to a 64-bit boundary.
Both changes were originally suggested by Eric Dumazet.
Signed-off-by: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Suggested-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: Brian Norris <computersforpeace@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/string.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
diff -puN lib/string.c~string-memchr_inv-speed-improvements lib/string.c
--- a/lib/string.c~string-memchr_inv-speed-improvements
+++ a/lib/string.c
@@ -785,12 +785,24 @@ void *memchr_inv(const void *start, int
if (bytes <= 16)
return check_bytes8(start, value, bytes);
- value64 = value | value << 8 | value << 16 | value << 24;
- value64 = (value64 & 0xffffffff) | value64 << 32;
- prefix = 8 - ((unsigned long)start) % 8;
+ value64 = value;
+#if defined(ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
+ value64 *= 0x0101010101010101;
+#elif defined(ARCH_HAS_FAST_MULTIPLIER)
+ value64 *= 0x01010101;
+ value64 |= value64 << 32;
+#else
+ value64 |= value64 << 8;
+ value64 |= value64 << 16;
+ value64 |= value64 << 32;
+#endif
+ prefix = (unsigned long)start % 8;
if (prefix) {
- u8 *r = check_bytes8(start, value, prefix);
+ u8 *r;
+
+ prefix = 8 - prefix;
+ r = check_bytes8(start, value, prefix);
if (r)
return r;
start += prefix;
_
Subject: Subject: string: memchr_inv speed improvements
Patches currently in -mm which might be from akinobu.mita@xxxxxxxxx are
xtensa-fix-memscan.patch
linux-next.patch
ocfs2-use-find_last_bit.patch
ocfs2-use-bitmap_weight.patch
drivers-scsi-hpsac-use-find_first_zero_bit.patch
bitops-rename-for_each_set_bit_cont-in-favor-of-analogous-listh-function.patch
bitops-remove-for_each_set_bit_cont.patch
bitops-introduce-for_each_clear_bit.patch
mtd-use-for_each_clear_bit.patch
s390-char-use-for_each_clear_bit.patch
uwb-use-for_each_clear_bit.patch
x86-use-for_each_clear_bit_from.patch
string-memchr_inv-speed-improvements.patch
sysctl-use-bitmap-library-functions.patch
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