Messages in this thread | | | Subject | Re: [PATCH] arm64: Implement optimised IP checksum helpers | From | Luke Starrett <> | Date | Thu, 12 May 2016 11:34:37 -0400 |
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Hi Robin,
I pulled this in to a userspace test app expecting that the __uint128_t type might cause GCC to emit 'ldp'. Seems like that was that your intent based on your commit note. Instead I see two 64b loads (ldr Xn), and a single 32b load (ldr Wn) for the trailing 4B. This was with Linaro GCC 4.9-2015.06.
Otherwise, the C cycle count looks good enough compared to the asm version.
Thanks,
Luke
On 5/12/2016 10:26 AM, Robin Murphy wrote: > 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> > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > > Having spent an evening poring over disassembler output, it turns out > that there's really no need to drop into asm for this, hurrah! I've > taken it for a spin on both big and little-endian, with no ill effects. > > arch/arm64/include/asm/checksum.h | 49 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 49 insertions(+) > create mode 100644 arch/arm64/include/asm/checksum.h > > diff --git a/arch/arm64/include/asm/checksum.h b/arch/arm64/include/asm/checksum.h > new file mode 100644 > index 000000000000..7e975ffce837 > --- /dev/null > +++ b/arch/arm64/include/asm/checksum.h > @@ -0,0 +1,49 @@ > +/* > + * 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 > + > +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 */
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