lib/libc/amd64/string/strlen.S: add amd64 baseline kernel
This performs very well. x86-64-v3 and x86-64-v4 kernels were written, too, but performed worse than the baseline kernel on short strings. These may be added at a future point in time if the performance issues can be fixed. os: FreeBSD arch: amd64 cpu: 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz │ strlen_scalar.out │ strlen_baseline.out │ │ B/s │ B/s vs base │ Short 1.667Gi ± 1% 2.676Gi ± 1% +60.55% (p=0.000 n=20) Mid 5.459Gi ± 1% 8.756Gi ± 1% +60.39% (p=0.000 n=20) Long 15.34Gi ± 0% 52.27Gi ± 0% +240.64% (p=0.000 n=20) geomean 5.188Gi 10.70Gi +106.24% Sponsored by: The FreeBSD Foundation Approved by: kib Reviewed by: mjg jrtc27 Differential Revision: https://reviews.freebsd.org/D40693
This commit is contained in:
parent
ad2fac552c
commit
d8385768fb
@ -1,11 +1,18 @@
|
||||
/*
|
||||
/*-
|
||||
* Written by Mateusz Guzik <mjg@freebsd.org>
|
||||
* Copyright (c) 2023 The FreeBSD Foundation
|
||||
*
|
||||
* Portions of this software were developed by Robert Clausecker
|
||||
* <fuz@FreeBSD.org> under sponsorship from the FreeBSD Foundation.
|
||||
*
|
||||
* Public domain.
|
||||
*/
|
||||
|
||||
#include <machine/asm.h>
|
||||
__FBSDID("$FreeBSD$");
|
||||
|
||||
#include "amd64_archlevel.h"
|
||||
|
||||
/*
|
||||
* Note: this routine was written with kernel use in mind (read: no simd),
|
||||
* it is only present in userspace as a temporary measure until something
|
||||
@ -14,6 +21,11 @@ __FBSDID("$FreeBSD$");
|
||||
|
||||
#define ALIGN_TEXT .p2align 4,0x90 /* 16-byte alignment, nop filled */
|
||||
|
||||
ARCHFUNCS(strlen)
|
||||
ARCHFUNC(strlen, scalar)
|
||||
ARCHFUNC(strlen, baseline)
|
||||
ENDARCHFUNCS(strlen)
|
||||
|
||||
/*
|
||||
* strlen(string)
|
||||
* %rdi
|
||||
@ -30,7 +42,7 @@ __FBSDID("$FreeBSD$");
|
||||
*
|
||||
* The latter contains a 32-bit variant of the same algorithm coded in assembly for i386.
|
||||
*/
|
||||
ENTRY(strlen)
|
||||
ARCHENTRY(strlen, scalar)
|
||||
movabsq $0xfefefefefefefeff,%r8
|
||||
movabsq $0x8080808080808080,%r9
|
||||
|
||||
@ -76,6 +88,46 @@ ENTRY(strlen)
|
||||
leaq (%rcx,%rdi),%rax
|
||||
subq %r10,%rax
|
||||
ret
|
||||
END(strlen)
|
||||
ARCHEND(strlen, scalar)
|
||||
|
||||
ARCHENTRY(strlen, baseline)
|
||||
mov %rdi, %rcx
|
||||
pxor %xmm1, %xmm1
|
||||
and $~0xf, %rdi # align string
|
||||
pcmpeqb (%rdi), %xmm1 # compare head (with junk before string)
|
||||
mov %rcx, %rsi # string pointer copy for later
|
||||
and $0xf, %ecx # amount of bytes rdi is past 16 byte alignment
|
||||
pmovmskb %xmm1, %eax
|
||||
add $32, %rdi # advance to next iteration
|
||||
shr %cl, %eax # clear out matches in junk bytes
|
||||
test %eax, %eax # any match? (can't use ZF from SHR as CL=0 is possible)
|
||||
jnz 2f
|
||||
|
||||
ALIGN_TEXT
|
||||
1: pxor %xmm1, %xmm1
|
||||
pcmpeqb -16(%rdi), %xmm1 # find NUL bytes
|
||||
pmovmskb %xmm1, %eax
|
||||
test %eax, %eax # were any NUL bytes present?
|
||||
jnz 3f
|
||||
|
||||
/* the same unrolled once more */
|
||||
pxor %xmm1, %xmm1
|
||||
pcmpeqb (%rdi), %xmm1
|
||||
pmovmskb %xmm1, %eax
|
||||
add $32, %rdi # advance to next iteration
|
||||
test %eax, %eax
|
||||
jz 1b
|
||||
|
||||
/* match found in loop body */
|
||||
sub $16, %rdi # undo half the advancement
|
||||
3: tzcnt %eax, %eax # find the first NUL byte
|
||||
sub %rsi, %rdi # string length until beginning of (%rdi)
|
||||
lea -16(%rdi, %rax, 1), %rax # that plus loc. of NUL byte: full string length
|
||||
ret
|
||||
|
||||
/* match found in head */
|
||||
2: tzcnt %eax, %eax # compute string length
|
||||
ret
|
||||
ARCHEND(strlen, baseline)
|
||||
|
||||
.section .note.GNU-stack,"",%progbits
|
||||
|
Loading…
Reference in New Issue
Block a user