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arm64: Implement optimised IP checksum helpers

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AArch64 is capable of 128-bit memory accesses without alignment
restrictions, which makes it both possible and highly practical to slurp
up a typical 20-byte IP header in just 2 loads. Implement our own
version of ip_fast_checksum() to take advantage of that, resulting in
considerably fewer instructions and memory accesses than the generic
version. We can also get more optimal code generation for csum_fold() by
defining it a slightly different way round from the generic version, so
throw that into the mix too.

Suggested-by: Luke Starrett <luke.starrett@broadcom.com>
Acked-by: Luke Starrett <luke.starrett@broadcom.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Robin Murphy 2016-05-31 18:04:40 +01:00 committed by Catalin Marinas
parent 33688abb28
commit 0e455d8e80
2 changed files with 51 additions and 1 deletions
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1
arch/arm64/include/asm/Kbuild
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@ -1,6 +1,5 @@
generic-y += bug.h
generic-y += bugs.h
generic-y += checksum.h
generic-y += clkdev.h
generic-y += cputime.h
generic-y += current.h

51
arch/arm64/include/asm/checksum.h Normal file
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@ -0,0 +1,51 @@
/*
* Copyright (C) 2016 ARM Ltd.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef __ASM_CHECKSUM_H
#define __ASM_CHECKSUM_H
#include <linux/types.h>
static inline __sum16 csum_fold(__wsum csum)
{
u32 sum = (__force u32)csum;
sum += (sum >> 16) | (sum << 16);
return ~(__force __sum16)(sum >> 16);
}
#define csum_fold csum_fold
static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
{
__uint128_t tmp;
u64 sum;
tmp = *(const __uint128_t *)iph;
iph += 16;
ihl -= 4;
tmp += ((tmp >> 64) | (tmp << 64));
sum = tmp >> 64;
do {
sum += *(const u32 *)iph;
iph += 4;
} while (--ihl);
sum += ((sum >> 32) | (sum << 32));
return csum_fold(sum >> 32);
}
#define ip_fast_csum ip_fast_csum
#include <asm-generic/checksum.h>
#endif /* __ASM_CHECKSUM_H */