Re: checksum: add VSX fast path for POWER8/POWER9

["Cédric Le Goater" <clg@kaod.org>]

Hi,

On 2/7/26 23:31, jfiusdq wrote:
> Microbenchmark of the checksum function vs C version at different buffer sizes:
>
> 
> Results (GB/s, higher is better; speedup = VSX / scalar):
> 
> 64B: VSX 4.61 vs scalar 5.91 -> 0.78x (VSX slower for tiny buffers)
> 256B: VSX 10.91 vs scalar 7.57 -> 1.44x
> 1500B: VSX 13.88 vs scalar 6.89 -> 2.02x
> 16KB: VSX 14.53 vs scalar 6.96 -> 2.09x
> 64KB: VSX 15.15 vs scalar 6.85 -> 2.21x

Could you please share Microbenchmark ?

Thanks,

C.

  
> On Friday, February 6th, 2026 at 3:17 PM, Laurent Vivier <lvivier@redhat.com> wrote:
> 
>>
> 
>>
> 
>> On Thu, 05 Feb 2026 06:14:40 +0000, jfiusdq jfiusdq@proton.me wrote:
>>
> 
>>> Tested with podman on Debian 13 for a while and works ok. It's
>>> difficult to run all the tests on POWER but 505-networking-pasta.bats
>>> test suite passes.
>>> ---
>>> checksum.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++++--
>>> 1 file changed, 107 insertions(+), 3 deletions(-)
>>>
> 
>>> diff --git a/checksum.c b/checksum.c
>>> index 0c3837c..828f9ec 100644
>>> --- a/checksum.c
>>> +++ b/checksum.c
>>> @@ -281,7 +281,7 @@ void csum_icmp6(struct icmp6hdr *icmp6hr,
>>> icmp6hr->icmp6_cksum = csum(payload, dlen, psum);
>>> }
>>>
> 
>>> -#ifdef AVX2
>>> +#if defined(AVX2)
>>> #include <immintrin.h>
>>>
> 
>>> /**
>>> @@ -479,7 +479,111 @@ uint32_t csum_unfolded(const void *buf, size_t len, uint32_t init)
>>>
> 
>>> return init;
>>> }
>>> -#else /* AVX2 /
>>> +#elif defined(POWER9_VECTOR) || defined(POWER8_VECTOR)
>>> +#include <altivec.h>
>>> +
>>> +/*
>>> + * csum_vsx() - Compute 32-bit checksum using VSX SIMD instructions
>>> + * @buf: Input buffer
>>> + * @len: Input length
>>> + * @init: Initial 32-bit checksum, 0 for no pre-computed checksum
>>> + *
>>> + * Return: 32-bit checksum, not complemented, not folded
>>> + /
>>> +/ NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) /
>>> +attribute((optimize("-fno-strict-aliasing"))) / See csum_16b() */
>>> +static uint32_t csum_vsx(const void buf, size_t len, uint32_t init)
>>> +{
>>> + const uint8_t p = buf;
>>> + vector unsigned int sum_even = vec_splat_u32(0);
>>> + vector unsigned int sum_odd = vec_splat_u32(0);
>>> + const vector unsigned short ones = vec_splat_u16(1);
>>> + uint64_t sum64 = init;
>>> +
>>> +#ifdef POWER9_VECTOR
>>> + while (len >= 64) {
>>> + vector unsigned char v0b = vec_vsx_ld(0, p);
>>> + vector unsigned char v1b = vec_vsx_ld(16, p);
>>> + vector unsigned char v2b = vec_vsx_ld(32, p);
>>> + vector unsigned char v3b = vec_vsx_ld(48, p);
>>> + vector unsigned short v0 = (vector unsigned short)v0b;
>>> + vector unsigned short v1 = (vector unsigned short)v1b;
>>> + vector unsigned short v2 = (vector unsigned short)v2b;
>>> + vector unsigned short v3 = (vector unsigned short)v3b;
>>> +
>>> + sum_even = vec_add(sum_even, vec_mule(v0, ones));
>>> + sum_odd = vec_add(sum_odd, vec_mulo(v0, ones));
>>> + sum_even = vec_add(sum_even, vec_mule(v1, ones));
>>> + sum_odd = vec_add(sum_odd, vec_mulo(v1, ones));
>>> + sum_even = vec_add(sum_even, vec_mule(v2, ones));
>>> + sum_odd = vec_add(sum_odd, vec_mulo(v2, ones));
>>> + sum_even = vec_add(sum_even, vec_mule(v3, ones));
>>> + sum_odd = vec_add(sum_odd, vec_mulo(v3, ones));
>>> +
>>> + p += 64;
>>> + len -= 64;
>>> + }
>>> +#endif
>>> +
>>> + while (len >= 32) {
>>> + vector unsigned char v0b = vec_vsx_ld(0, p);
>>> + vector unsigned char v1b = vec_vsx_ld(16, p);
>>> + vector unsigned short v0 = (vector unsigned short)v0b;
>>> + vector unsigned short v1 = (vector unsigned short)v1b;
>>> +
>>> + sum_even = vec_add(sum_even, vec_mule(v0, ones));
>>> + sum_odd = vec_add(sum_odd, vec_mulo(v0, ones));
>>> + sum_even = vec_add(sum_even, vec_mule(v1, ones));
>>> + sum_odd = vec_add(sum_odd, vec_mulo(v1, ones));
>>> +
>>> + p += 32;
>>> + len -= 32;
>>> + }
>>> +
>>> + while (len >= 16) {
>>> + vector unsigned char v0b = vec_vsx_ld(0, p);
>>> + vector unsigned short v0 = (vector unsigned short)v0b;
>>> +
>>> + sum_even = vec_add(sum_even, vec_mule(v0, ones));
>>> + sum_odd = vec_add(sum_odd, vec_mulo(v0, ones));
>>> +
>>> + p += 16;
>>> + len -= 16;
>>> + }
>>> +
>>> + {
>>> + vector unsigned int sum32 = vec_add(sum_even, sum_odd);
>>> + uint32_t partial[4] attribute((aligned(16)));
>>> +
>>> + vec_st(sum32, 0, partial);
>>> + sum64 += (uint64_t)partial[0] + partial[1] +
>>> + partial[2] + partial[3];
>>> + }
>>> +
>>> + sum64 += sum_16b(p, len);
>>> +
>>> + sum64 = (sum64 >> 32) + (sum64 & 0xffffffff);
>>> + sum64 += sum64 >> 32;
>>> +
>>> + return (uint32_t)sum64;
>>> +}
>>> +
>>> +/
>>> + * csum_unfolded() - Calculate the unfolded checksum of a data buffer.
>>> + *
>>> + * @buf: Input buffer
>>> + * @len: Input length
>>> + * @init: Initial 32-bit checksum, 0 for no pre-computed checksum
>>> + *
>>> + * Return: 32-bit unfolded checksum
>>> + /
>>> +/ NOLINTNEXTLINE(clang-diagnostic-unknown-attributes) /
>>> +attribute((optimize("-fno-strict-aliasing"))) / See csum_16b() /
>>> +uint32_t csum_unfolded(const void buf, size_t len, uint32_t init)
>>> +{
>>> + return csum_vsx(buf, len, init);
>>> +}
>>> +#else / !AVX2 && !POWER9_VECTOR && !POWER8_VECTOR /
>>> /
>>> * csum_unfolded() - Calculate the unfolded checksum of a data buffer.
>>> *
>>> @@ -495,7 +599,7 @@ uint32_t csum_unfolded(const void buf, size_t len, uint32_t init)
>>> {
>>> return sum_16b(buf, len) + init;
>>> }
>>> -#endif / !AVX2 /
>>> +#endif / !AVX2 && !POWER9_VECTOR && !POWER8_VECTOR */
>>>
> 
>>> /**
>>> * csum_iov_tail() - Calculate unfolded checksum for the tail of an IO vector
>>> --
>>> 2.52.0
>>
> 
>>
> 
>> Reviewed-by: Laurent Vivier lvivier@redhat.com