Re: [PATCH v3] arm64: lib: accelerate do_csum with NEON instruction

["huanglingyan (A)" <huanglingyan2@huawei.com>]

On 2019/1/6 16:26, Ard Biesheuvel wrote:
> On Sun, 6 Jan 2019 at 02:56, Lingyan Huang <huanglingyan2@huawei.com> wrote:
>> Function do_csum() in lib/checksum.c is used to compute checksum,
>> which is turned out to be slowly and costs a lot of resources.
>> Let's use neon instructions to accelerate the checksum computation
>> for arm64.
>>
>> ------
>> V2 ==> V3:
>>     only modify the arm64 codes instead of modifying headers
>>     under asm-generic and code in lib/checksum.c.
>> ------
>> ------
>> V1 ==> V2:
>>     Change NEON assembly code to NEON intrinsic code which is built
>>     on top of arm_neon.h to avoid dropping into assembly.
>> ------
>>
> Please put the changelog between the --- below and the diffstat
ok
>> Here is the comparison results of function ip_compute_csum() between
>> general do_csum() and neon instruction do_csum(). The test platform
>> is HUAWEI 1620 server with TAISHAN cores.
>>
>>         len(1000cycle)      general(ns)        do_csum_neon(ns)
>>           64B:                58060                 59460
>>          128B:                82930                 83930
>>          256B:               132480                 73570
>>          512B:               230100                 86230
>>         1024B:               426600                 98200
>>
> Again, very nice performance. How did you test for correctness?

I compare my computing results with the results of do_csum() function in lib/checksum.c to ensure its correctness.

>> Cc: Catalin Marinas <catalin.marinas@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Signed-off-by: Lingyan Huang <huanglingyan2@huawei.com>
>> ---
>>  arch/arm64/include/asm/checksum.h |   5 ++
>>  arch/arm64/lib/Makefile           |   8 +--
>>  arch/arm64/lib/checksum.c         |  26 ++++++++
>>  arch/arm64/lib/do_csum.c          | 136 ++++++++++++++++++++++++++++++++++++++
>>  4 files changed, 171 insertions(+), 4 deletions(-)
>>  create mode 100644 arch/arm64/lib/checksum.c
>>  create mode 100644 arch/arm64/lib/do_csum.c
>>
>> diff --git a/arch/arm64/include/asm/checksum.h b/arch/arm64/include/asm/checksum.h
>> index 0b6f5a7..7acd713 100644
>> --- a/arch/arm64/include/asm/checksum.h
>> +++ b/arch/arm64/include/asm/checksum.h
>> @@ -26,6 +26,10 @@ static inline __sum16 csum_fold(__wsum csum)
>>  }
>>  #define csum_fold csum_fold
>>
>> +#define do_csum do_csum
>> +unsigned int do_csum(const unsigned char *buff, int len);
>> +extern unsigned int do_csum_arm(const unsigned char *buff, int len);
>> +
>>  static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
>>  {
>>         __uint128_t tmp;
>> @@ -46,6 +50,7 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
>>  }
>>  #define ip_fast_csum ip_fast_csum
>>
>> +
> Drop this whitespace-only change
OK
>>  #include <asm-generic/checksum.h>
>>
>>  #endif /* __ASM_CHECKSUM_H */
>> diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
>> index 5540a16..c0b5b8c 100644
>> --- a/arch/arm64/lib/Makefile
>> +++ b/arch/arm64/lib/Makefile
>> @@ -3,12 +3,12 @@ lib-y         := clear_user.o delay.o copy_from_user.o                \
>>                    copy_to_user.o copy_in_user.o copy_page.o            \
>>                    clear_page.o memchr.o memcpy.o memmove.o memset.o    \
>>                    memcmp.o strcmp.o strncmp.o strlen.o strnlen.o       \
>> -                  strchr.o strrchr.o tishift.o
>> +                  strchr.o strrchr.o tishift.o checksum.o
>>
>>  ifeq ($(CONFIG_KERNEL_MODE_NEON), y)
>> -obj-$(CONFIG_XOR_BLOCKS)       += xor-neon.o
>> -CFLAGS_REMOVE_xor-neon.o       += -mgeneral-regs-only
>> -CFLAGS_xor-neon.o              += -ffreestanding
>> +obj-y    += do_csum.o
> Please indent aligned with the others

I'm sorry i was so careless

>> +CFLAGS_REMOVE_do_csum.o        += -mgeneral-regs-only
>> +CFLAGS_do_csum.o               += -ffreestanding
>>  endif
>>
>>  # Tell the compiler to treat all general purpose registers (with the
>> diff --git a/arch/arm64/lib/checksum.c b/arch/arm64/lib/checksum.c
>> new file mode 100644
>> index 0000000..15a31bb
>> --- /dev/null
>> +++ b/arch/arm64/lib/checksum.c
>> @@ -0,0 +1,26 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + *
>> + * Authors: Lingyan Huang <huanglingyan2@huawei.com>
>> + * Copyright (C) 2018 Hisilicon, Inc. All Rights Reserved.
>> + *
>> + * Generic C or neon implementation of do_csum operations.
>> + * Choose faster neon instructions when NEON is supported.
>> + *
>> + */
>> +
>> +#include <asm/neon.h>
>> +#include <asm/simd.h>
>> +#include <asm/checksum.h>
>> +
>> +#define CSUM_NEON_THRESHOLD 128
>> +
>> +unsigned int do_csum(const unsigned char *buff, int len)
>> +{
>> +#ifdef CONFIG_KERNEL_MODE_NEON
>> +       if (len >= CSUM_NEON_THRESHOLD)
> Please change this into
>
> if (IS_ENABLED(CONFIG_KERNEL_MODE_NEON) &&
>     len >= CSUM_NEON_THRESHOLD &&
>     may_use_simd()) {
>         kernel_neon_begin();
>         res = do_csum_neon(buff, len);
>         kernel_neon_end();
>     }
>
> and drop the intermediate do_csum_arm()
>
>> +               return do_csum_arm(buff, len);
>> +#endif  /* CONFIG_KERNEL_MODE_NEON */
> No else? What happens if len < CSUM_NEON_THRESHOLD ?
>
>> +#undef do_csum
> Can we drop this?
Using NEON instructions will bring some costs. The spending maybe introduced when reservering/restoring
neon registers with kernel_neon_begin()/kernel_neon_end(). Therefore NEON code is Only used when
the length exceeds CSUM_NEON_THRESHOLD. General do csum() codes in lib/checksum.c will be used in
shorter length. To achieve this goal, I use the "#undef do_csum" in else clause to have the oppotunity to
utilize the general codes.

However, this solution may not be a standard way. Is there any other solutions to achieve this goal?

> Codes in lib/checksum.c.

#ifndef do_csum
static unsigned int do_csum(const unsigned char *buff, int len)
{
……
}

>> +       return 0;
>> +}
>> diff --git a/arch/arm64/lib/do_csum.c b/arch/arm64/lib/do_csum.c
>> new file mode 100644
>> index 0000000..893583f
>> --- /dev/null
>> +++ b/arch/arm64/lib/do_csum.c
>> @@ -0,0 +1,136 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Authors: Lingyan Huang <huanglingyan2@huawei.com>
>> + * Copyright (C) 2018 Hisilicon, Inc. All Rights Reserved.
>> + *
>> + * Generic C or neon implementation of do_csum operations.
>> + * Choose faster neon instructions when NEON is supported.
>> + *
>> + */
>> +
>> +#include <asm/neon.h>
>> +#include <asm/simd.h>
>> +#include <asm/checksum.h>
>> +#include <asm/byteorder.h>
>> +#include <asm/neon-intrinsics.h>
>> +
>> +#define CSUM_NEON_THRESHOLD 128
> Drop this - it is not used in this file
OK
>> +#ifdef CONFIG_KERNEL_MODE_NEON
> This file is only built if KERNEL_MODE_NEON=y so the #ifdef can be dropped
OK
>> +static inline u32 from64to16(u64 x)
>> +{
>> +       /* add up 32-bit and 32-bit for 32+c bit */
>> +       x = (x & 0xffffffff) + (x >> 32);
>> +       /* add up carry.. */
>> +       x = (x & 0xffffffff) + (x >> 32);
>> +       /* add up 16-bit and 16-bit for 16+c bit */
>> +       x = ((u32)x & 0xffff) + ((u32)x >> 16);
>> +       /* add up carry.. */
>> +       x = ((u32)x & 0xffff) + ((u32)x >> 16);
>> +       return x;
>> +}
>> +
>> +unsigned int do_csum_neon(const unsigned char *buff, int len)
>> +{
>> +       unsigned int odd, count;
>> +       uint64_t result = 0;
>> +       unsigned int count64;
>> +       uint32x4_t vzero = (uint32x4_t){0, 0, 0, 0};
>> +
>> +       register uint32x4_t v0, v1, v2, v3;
>> +
>> +       if (unlikely(len <= 0))
>> +               return result;
>> +
>> +       odd = 1 & (unsigned long)buff;
>> +       if (unlikely(odd)) {
>> +               result = *buff;
>> +               len--;
>> +               buff++;
>> +       }
>> +
>> +       count = len >> 1;
>> +       if (count) {
>> +               if (2 & (unsigned long)buff) {
>> +                       result += *(unsigned short *)buff;
>> +                       count--;
>> +                       len -= 2;
>> +                       buff += 2;
>> +               }
>> +               count >>= 1;            /* nr of 32-bit words.. */
>> +               if (count) {
>> +                       if (4 & (unsigned long)buff) {
>> +                               result += *(unsigned int *)buff;
>> +                               count--;
>> +                               len -= 4;
>> +                               buff += 4;
>> +                       }
>> +                       count >>= 1;    /* nr of 64-bit words.. */
>> +
>> +                       v0 = vzero;
>> +                       v1 = vzero;
>> +                       v2 = vzero;
>> +                       v3 = vzero;
>> +
>> +                       count64 = count >> 3;  /* compute 64 Byte circle */
>> +                       while (count64) {
>> +                               v0 = vpadalq_u16(v0,
>> +                                       vld1q_u16((uint16_t *)buff + 0));
>> +                               v1 = vpadalq_u16(v1,
>> +                                       vld1q_u16((uint16_t *)buff + 8));
>> +                               v2 = vpadalq_u16(v2,
>> +                                       vld1q_u16((uint16_t *)buff + 16));
>> +                               v3 = vpadalq_u16(v3,
>> +                                       vld1q_u16((uint16_t *)buff + 24));
>> +                               buff += 64;
>> +                               count64--;
>> +                       }
>> +                       v0 = vaddq_u32(v0, v1);
>> +                       v2 = vaddq_u32(v2, v3);
>> +                       v0 = vaddq_u32(v0, v2);
>> +
>> +                       count %= 8;
>> +                       while (count >= 2) { /* compute 16 byte circle */
>> +                               v0 = vpadalq_u16(v0,
>> +                                       vld1q_u16((uint16_t *)buff + 0));
>> +                               buff += 16;
>> +                               count -= 2;
>> +                       }
>> +
>> +                       result += vgetq_lane_u32(v0, 0);
>> +                       result += vgetq_lane_u32(v0, 1);
>> +                       result += vgetq_lane_u32(v0, 2);
>> +                       result += vgetq_lane_u32(v0, 3);
>> +                       if (count & 1) {
>> +                               result += *(unsigned long long *)buff;
>> +                               buff += 8;
>> +                       }
>> +                       if (len & 4) {
>> +                               result += *(unsigned int *)buff;
>> +                               buff += 4;
>> +                       }
>> +               }
>> +               if (len & 2) {
>> +                       result += *(unsigned short *)buff;
>> +                       buff += 2;
>> +               }
>> +       }
>> +       if (len & 1)
>> +               result += *buff;
>> +       result = from64to16(result);
>> +       if (odd)
>> +               result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
>> +       return result;
>> +}
>> +#endif
>> +
>> +
>> +unsigned int do_csum_arm(const unsigned char *buff, int len)
>> +{
>> +       unsigned int res;
>> +
>> +       kernel_neon_begin();
>> +       res = do_csum_neon(buff, len);
>> +       kernel_neon_end();
>> +       return res;
>> +}
> As I said above, please drop this intermediate function and fold the
> logic into do_csum()
OK
> .
>



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