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Subject[PATCH] lib/x86: Optimise csum_partial of buffers that are not multiples of 8 bytes.
Date

Add in the trailing bytes first so that there is no need to worry
about the sum exceeding 64 bits.

Signed-off-by: David Laight <david.laight@aculab.com>
---

This ought to be faster - because of all the removed 'adc $0'.
Guessing how fast x86 code will run is hard!
There are other ways of handing buffers that are shorter than 8 bytes,
but I'd rather hope they don't happen in any hot paths.

Note - I've not even compile tested it.
(But have tested an equivalent change before.)

arch/x86/lib/csum-partial_64.c | 55 ++++++++++++----------------------
1 file changed, 19 insertions(+), 36 deletions(-)

diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
index abf819dd8525..fbcc073fc2b5 100644
--- a/arch/x86/lib/csum-partial_64.c
+++ b/arch/x86/lib/csum-partial_64.c
@@ -37,6 +37,24 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
u64 temp64 = (__force u64)sum;
unsigned result;

+ if (len & 7) {
+ if (unlikely(len < 8)) {
+ /* Avoid falling off the start of the buffer */
+ if (len & 4) {
+ temp64 += *(u32 *)buff;
+ buff += 4;
+ }
+ if (len & 2) {
+ temp64 += *(u16 *)buff;
+ buff += 2;
+ }
+ if (len & 1)
+ temp64 += *(u8 *)buff;
+ goto reduce_to32;
+ }
+ temp64 += *(u64 *)(buff + len - 8) << (8 - (len & 7)) * 8;
+ }
+
while (unlikely(len >= 64)) {
asm("addq 0*8(%[src]),%[res]\n\t"
"adcq 1*8(%[src]),%[res]\n\t"
@@ -82,43 +100,8 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
: "memory");
buff += 8;
}
- if (len & 7) {
-#ifdef CONFIG_DCACHE_WORD_ACCESS
- unsigned int shift = (8 - (len & 7)) * 8;
- unsigned long trail;
-
- trail = (load_unaligned_zeropad(buff) << shift) >> shift;

- asm("addq %[trail],%[res]\n\t"
- "adcq $0,%[res]"
- : [res] "+r" (temp64)
- : [trail] "r" (trail));
-#else
- if (len & 4) {
- asm("addq %[val],%[res]\n\t"
- "adcq $0,%[res]"
- : [res] "+r" (temp64)
- : [val] "r" ((u64)*(u32 *)buff)
- : "memory");
- buff += 4;
- }
- if (len & 2) {
- asm("addq %[val],%[res]\n\t"
- "adcq $0,%[res]"
- : [res] "+r" (temp64)
- : [val] "r" ((u64)*(u16 *)buff)
- : "memory");
- buff += 2;
- }
- if (len & 1) {
- asm("addq %[val],%[res]\n\t"
- "adcq $0,%[res]"
- : [res] "+r" (temp64)
- : [val] "r" ((u64)*(u8 *)buff)
- : "memory");
- }
-#endif
- }
+reduce_to32:
result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
return (__force __wsum)result;
}
--
2.17.1
-
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