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SubjectRe: [PATCH v1] x86/lib: Optimize 8x loop and memory clobbers in csum_partial.c
On Fri, Nov 26, 2021 at 11:50 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> Bright :) but it will need a BMI support check.

Yes, probably not worth the pain.

>
> I actually get better performance in hyperthread benchmarks with 2 accum:
>
> Used:
>
> u64 res;
> temp64 = (__force uint64_t)sum;
> asm("movq 0*8(%[src]),%[res]\n\t"
> "addq 1*8(%[src]),%[res]\n\t"
> "adcq 2*8(%[src]),%[res]\n\t"
> "adcq $0, %[res]\n"
> "addq 3*8(%[src]),%[temp64]\n\t"
> "adcq 4*8(%[src]),%[temp64]\n\t"
> "adcq %[res], %[temp64]\n\t"
> "mov %k[temp64],%k[res]\n\t"
> "rorx $32,%[temp64],%[temp64]\n\t"
> "adcl %k[temp64],%k[res]\n\t"
> "adcl $0,%k[res]"
> : [temp64] "+r"(temp64), [res] "=&r"(res)
> : [src] "r"(buff)
> : "memory");
> return (__force __wsum)res;
>
> w/ hyperthread:
> size, 2acc lat, 1acc lat, 2acc tput, 1acc tput
> 40, 6.511, 7.863, 6.177, 6.157
>
> w/o hyperthread:
> size, 2acc lat, 1acc lat, 2acc tput, 1acc tput
> 40, 5.577, 6.764, 3.150, 3.210

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