| Message ID | ba9cf5bf84b8adc766f7f7511dda8cb501cd4101.1464693619.git.robin.murphy@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Robin, On 31/05/16 12:22, 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> > Acked-by: Luke Starrett <luke.starrett@broadcom.com> > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > > Minor changes: include types.h for correctness, add Luke's ack. > > arch/arm64/include/asm/checksum.h | 51 +++++++++++++++++++++++++++++++++++++++ Maybe a nit, don't you need to remove the 'generic-y += checksum.h' line from arch/arm64/include/asm/Kbuild to avoid the generated version being created too? [0] The compiler on my box picks your header in preference to the generated one, but [1] suggests it isn't to be trusted! Thanks, James [0] d8ecc5cd8e22 ("kbuild: asm-generic support") [1] https://lkml.org/lkml/2016/5/23/78
Hi James, On 31/05/16 15:24, James Morse wrote: > Hi Robin, > > On 31/05/16 12:22, 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> >> Acked-by: Luke Starrett <luke.starrett@broadcom.com> >> Signed-off-by: Robin Murphy <robin.murphy@arm.com> >> --- >> >> Minor changes: include types.h for correctness, add Luke's ack. >> >> arch/arm64/include/asm/checksum.h | 51 +++++++++++++++++++++++++++++++++++++++ > > Maybe a nit, don't you need to remove the 'generic-y += checksum.h' line from > arch/arm64/include/asm/Kbuild to avoid the generated version being created too? [0] I guess you skimmed the very end of the patch ;) +#include <asm-generic/checksum.h> > The compiler on my box picks your header in preference to the generated one, but > [1] suggests it isn't to be trusted! We only cherry-pick a couple of functions to optimise, so not building the generic file would necessitate copy-pasting the rest of it. I'd hope this pattern is sufficiently robust, since it's already in use on a number of other architectures! AFAICS [1] only applies when the generic file shouldn't be built at all, so cross fingers we're probably OK. Robin. > Thanks, > > James > > [0] d8ecc5cd8e22 ("kbuild: asm-generic support") > [1] https://lkml.org/lkml/2016/5/23/78 > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >
On 31/05/16 15:39, Robin Murphy wrote: > Hi James, > > On 31/05/16 15:24, James Morse wrote: >> Hi Robin, >> >> On 31/05/16 12:22, 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> >>> Acked-by: Luke Starrett <luke.starrett@broadcom.com> >>> Signed-off-by: Robin Murphy <robin.murphy@arm.com> >>> --- >>> >>> Minor changes: include types.h for correctness, add Luke's ack. >>> >>> arch/arm64/include/asm/checksum.h | 51 >>> +++++++++++++++++++++++++++++++++++++++ >> >> Maybe a nit, don't you need to remove the 'generic-y += checksum.h' >> line from >> arch/arm64/include/asm/Kbuild to avoid the generated version being >> created too? [0] > > I guess you skimmed the very end of the patch ;) > > +#include <asm-generic/checksum.h> Oh wait, I'm being a massive idiot - include/asm-generic is not the same thing as arch/arm/include/generated/asm, is it? I see what you mean now, and yes it probably does want fixing... Sorry! Robin. >> The compiler on my box picks your header in preference to the >> generated one, but >> [1] suggests it isn't to be trusted! > > We only cherry-pick a couple of functions to optimise, so not building > the generic file would necessitate copy-pasting the rest of it. I'd hope > this pattern is sufficiently robust, since it's already in use on a > number of other architectures! AFAICS [1] only applies when the generic > file shouldn't be built at all, so cross fingers we're probably OK. > > Robin. > >> Thanks, >> >> James >> >> [0] d8ecc5cd8e22 ("kbuild: asm-generic support") >> [1] https://lkml.org/lkml/2016/5/23/78 >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >> > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff --git a/arch/arm64/include/asm/checksum.h b/arch/arm64/include/asm/checksum.h new file mode 100644 index 000000000000..09f65339d66d --- /dev/null +++ b/arch/arm64/include/asm/checksum.h @@ -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 */