Re: [PATCH v3] LoongArch: add checksum optimization for 64-bit system

[maobibo]

在 2023/3/1 20:54, Huacai Chen 写道:
> Hi, Bibo,
> 
> I found the version here [1] provides more functions than this one. So
> is it possible to take advantages from both versions?
csum and copy user will take me much time:(  Just for csum there is no obvious
results between uint128 and interleave method, it depends on compiler version
also. I want to re-investigate two methods after LoongArch gcc optimization
version is stable.

Three methods are tested on LoongArch 3A5000 machine: uint128/asm/interleave
methods, interleave method gets double performance on x86 box compared with
uint128 method, however no better than LoongArch 3A5000 machine and one
ARM64 machine. The three test methods are listed at website:
https://github.com/bibo-mao/bench/tree/master/csum

Here is the result on 3A5000 machine, time unit is us, smaller for
better performance.

buf size    loops      uint128      asm       interleave
4096       0x100000     279824     373401     291508
1472       0x100000     109137     138224     106035
250        0x100000     29008      35838      23408
40         0x100000     9789       23408      9122

Regards
Bibo, mao
> 
> [1] https://github.com/loongson/linux/commit/92a6df48ccb73dd2c3dc1799add08adf0e0b0deb
> 
> Huacai
> 
> On Thu, Feb 16, 2023 at 9:09 PM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
>>
>> loongArch platform is 64-bit system, which supports 8 bytes memory
>> accessing, generic checksum function uses 4 byte memory access.
>> This patch adds 8-bytes memory access optimization for checksum
>> function on loongArch. And the code comes from arm64 system.
>>
>> When network hw checksum is disabled, iperf performance improves
>> about 10% with this patch.
>>
>> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
>> ---
>> Changelog:
>> v3: modify function accumulate() to handle better on loongarch platform,
>>     maybe it's compiler optimization issue.
>> v2: use rotation API in function csum_fold to reduce one instruction.
>> ---
>>  arch/loongarch/include/asm/checksum.h |  65 ++++++++++++
>>  arch/loongarch/lib/Makefile           |   2 +-
>>  arch/loongarch/lib/csum.c             | 141 ++++++++++++++++++++++++++
>>  3 files changed, 207 insertions(+), 1 deletion(-)
>>  create mode 100644 arch/loongarch/include/asm/checksum.h
>>  create mode 100644 arch/loongarch/lib/csum.c
>>
>> diff --git a/arch/loongarch/include/asm/checksum.h b/arch/loongarch/include/asm/checksum.h
>> new file mode 100644
>> index 000000000000..8a7d368d801d
>> --- /dev/null
>> +++ b/arch/loongarch/include/asm/checksum.h
>> @@ -0,0 +1,65 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Copyright (C) 2016 ARM Ltd.
>> + * Copyright (C) 2023 Loongson Technology Corporation Limited
>> + */
>> +#ifndef __ASM_CHECKSUM_H
>> +#define __ASM_CHECKSUM_H
>> +
>> +#include <linux/in6.h>
>> +
>> +#define _HAVE_ARCH_IPV6_CSUM
>> +__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
>> +                       const struct in6_addr *daddr,
>> +                       __u32 len, __u8 proto, __wsum sum);
>> +
>> +/*
>> + * turns a 32-bit partial checksum (e.g. from csum_partial) into a
>> + * 1's complement 16-bit checksum.
>> + */
>> +static inline __sum16 csum_fold(__wsum sum)
>> +{
>> +       u32 tmp = (__force u32)sum;
>> +
>> +       /*
>> +        * swap the two 16-bit halves of sum
>> +        * if there is a carry from adding the two 16-bit halves,
>> +        * it will carry from the lower half into the upper half,
>> +        * giving us the correct sum in the upper half.
>> +        */
>> +       return (__force __sum16)(~(tmp + rol32(tmp, 16)) >> 16);
>> +}
>> +#define csum_fold csum_fold
>> +
>> +/*
>> + * This is a version of ip_compute_csum() optimized for IP headers,
>> + * which always checksum on 4 octet boundaries.  ihl is the number
>> + * of 32-bit words and is always >= 5.
>> + */
>> +static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
>> +{
>> +       __uint128_t tmp;
>> +       u64 sum;
>> +       int n = ihl; /* we want it signed */
>> +
>> +       tmp = *(const __uint128_t *)iph;
>> +       iph += 16;
>> +       n -= 4;
>> +       tmp += ((tmp >> 64) | (tmp << 64));
>> +       sum = tmp >> 64;
>> +       do {
>> +               sum += *(const u32 *)iph;
>> +               iph += 4;
>> +       } while (--n > 0);
>> +
>> +       sum += ror64(sum, 32);
>> +       return csum_fold((__force __wsum)(sum >> 32));
>> +}
>> +#define ip_fast_csum ip_fast_csum
>> +
>> +extern unsigned int do_csum(const unsigned char *buff, int len);
>> +#define do_csum do_csum
>> +
>> +#include <asm-generic/checksum.h>
>> +
>> +#endif /* __ASM_CHECKSUM_H */
>> diff --git a/arch/loongarch/lib/Makefile b/arch/loongarch/lib/Makefile
>> index 40bde632900f..6ba6df411f90 100644
>> --- a/arch/loongarch/lib/Makefile
>> +++ b/arch/loongarch/lib/Makefile
>> @@ -4,4 +4,4 @@
>>  #
>>
>>  lib-y  += delay.o memset.o memcpy.o memmove.o \
>> -          clear_user.o copy_user.o dump_tlb.o unaligned.o
>> +          clear_user.o copy_user.o dump_tlb.o unaligned.o csum.o
>> diff --git a/arch/loongarch/lib/csum.c b/arch/loongarch/lib/csum.c
>> new file mode 100644
>> index 000000000000..a5e84b403c3b
>> --- /dev/null
>> +++ b/arch/loongarch/lib/csum.c
>> @@ -0,0 +1,141 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +// Copyright (C) 2019-2020 Arm Ltd.
>> +
>> +#include <linux/compiler.h>
>> +#include <linux/kasan-checks.h>
>> +#include <linux/kernel.h>
>> +
>> +#include <net/checksum.h>
>> +
>> +static u64 accumulate(u64 sum, u64 data)
>> +{
>> +       sum += data;
>> +       if (sum < data)
>> +               sum += 1;
>> +       return sum;
>> +}
>> +
>> +/*
>> + * We over-read the buffer and this makes KASAN unhappy. Instead, disable
>> + * instrumentation and call kasan explicitly.
>> + */
>> +unsigned int __no_sanitize_address do_csum(const unsigned char *buff, int len)
>> +{
>> +       unsigned int offset, shift, sum;
>> +       const u64 *ptr;
>> +       u64 data, sum64 = 0;
>> +
>> +       if (unlikely(len == 0))
>> +               return 0;
>> +
>> +       offset = (unsigned long)buff & 7;
>> +       /*
>> +        * This is to all intents and purposes safe, since rounding down cannot
>> +        * result in a different page or cache line being accessed, and @buff
>> +        * should absolutely not be pointing to anything read-sensitive. We do,
>> +        * however, have to be careful not to piss off KASAN, which means using
>> +        * unchecked reads to accommodate the head and tail, for which we'll
>> +        * compensate with an explicit check up-front.
>> +        */
>> +       kasan_check_read(buff, len);
>> +       ptr = (u64 *)(buff - offset);
>> +       len = len + offset - 8;
>> +
>> +       /*
>> +        * Head: zero out any excess leading bytes. Shifting back by the same
>> +        * amount should be at least as fast as any other way of handling the
>> +        * odd/even alignment, and means we can ignore it until the very end.
>> +        */
>> +       shift = offset * 8;
>> +       data = *ptr++;
>> +       data = (data >> shift) << shift;
>> +
>> +       /*
>> +        * Body: straightforward aligned loads from here on (the paired loads
>> +        * underlying the quadword type still only need dword alignment). The
>> +        * main loop strictly excludes the tail, so the second loop will always
>> +        * run at least once.
>> +        */
>> +       while (unlikely(len > 64)) {
>> +               __uint128_t tmp1, tmp2, tmp3, tmp4;
>> +
>> +               tmp1 = *(__uint128_t *)ptr;
>> +               tmp2 = *(__uint128_t *)(ptr + 2);
>> +               tmp3 = *(__uint128_t *)(ptr + 4);
>> +               tmp4 = *(__uint128_t *)(ptr + 6);
>> +
>> +               len -= 64;
>> +               ptr += 8;
>> +
>> +               /* This is the "don't dump the carry flag into a GPR" idiom */
>> +               tmp1 += (tmp1 >> 64) | (tmp1 << 64);
>> +               tmp2 += (tmp2 >> 64) | (tmp2 << 64);
>> +               tmp3 += (tmp3 >> 64) | (tmp3 << 64);
>> +               tmp4 += (tmp4 >> 64) | (tmp4 << 64);
>> +               tmp1 = ((tmp1 >> 64) << 64) | (tmp2 >> 64);
>> +               tmp1 += (tmp1 >> 64) | (tmp1 << 64);
>> +               tmp3 = ((tmp3 >> 64) << 64) | (tmp4 >> 64);
>> +               tmp3 += (tmp3 >> 64) | (tmp3 << 64);
>> +               tmp1 = ((tmp1 >> 64) << 64) | (tmp3 >> 64);
>> +               tmp1 += (tmp1 >> 64) | (tmp1 << 64);
>> +               tmp1 = ((tmp1 >> 64) << 64) | sum64;
>> +               tmp1 += (tmp1 >> 64) | (tmp1 << 64);
>> +               sum64 = tmp1 >> 64;
>> +       }
>> +       while (len > 8) {
>> +               __uint128_t tmp;
>> +
>> +               sum64 = accumulate(sum64, data);
>> +               tmp = *(__uint128_t *)ptr;
>> +
>> +               len -= 16;
>> +               ptr += 2;
>> +
>> +               data = tmp >> 64;
>> +               sum64 = accumulate(sum64, tmp);
>> +       }
>> +       if (len > 0) {
>> +               sum64 = accumulate(sum64, data);
>> +               data = *ptr;
>> +               len -= 8;
>> +       }
>> +       /*
>> +        * Tail: zero any over-read bytes similarly to the head, again
>> +        * preserving odd/even alignment.
>> +        */
>> +       shift = len * -8;
>> +       data = (data << shift) >> shift;
>> +       sum64 = accumulate(sum64, data);
>> +
>> +       /* Finally, folding */
>> +       sum64 += (sum64 >> 32) | (sum64 << 32);
>> +       sum = sum64 >> 32;
>> +       sum += (sum >> 16) | (sum << 16);
>> +       if (offset & 1)
>> +               return (u16)swab32(sum);
>> +
>> +       return sum >> 16;
>> +}
>> +
>> +__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
>> +                       const struct in6_addr *daddr,
>> +                       __u32 len, __u8 proto, __wsum csum)
>> +{
>> +       __uint128_t src, dst;
>> +       u64 sum = (__force u64)csum;
>> +
>> +       src = *(const __uint128_t *)saddr->s6_addr;
>> +       dst = *(const __uint128_t *)daddr->s6_addr;
>> +
>> +       sum += (__force u32)htonl(len);
>> +       sum += (u32)proto << 24;
>> +       src += (src >> 64) | (src << 64);
>> +       dst += (dst >> 64) | (dst << 64);
>> +
>> +       sum = accumulate(sum, src >> 64);
>> +       sum = accumulate(sum, dst >> 64);
>> +
>> +       sum += ((sum >> 32) | (sum << 32));
>> +       return csum_fold((__force __wsum)(sum >> 32));
>> +}
>> +EXPORT_SYMBOL(csum_ipv6_magic);
>> --
>> 2.27.0
>>