mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-21 12:30:06 +00:00
elf: Optimize _dl_new_hash in dl-new-hash.h
Unroll slightly and enforce good instruction scheduling. This improves performance on out-of-order machines. The unrolling allows for pipelined multiplies. As well, as an optional sysdep, reorder the operations and prevent reassosiation for better scheduling and higher ILP. This commit only adds the barrier for x86, although it should be either no change or a win for any architecture. Unrolling further started to induce slowdowns for sizes [0, 4] but can help the loop so if larger sizes are the target further unrolling can be beneficial. Results for _dl_new_hash Benchmarked on Tigerlake: 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz Time as Geometric Mean of N=30 runs Geometric of all benchmark New / Old: 0.674 type, length, New Time, Old Time, New Time / Old Time fixed, 0, 2.865, 2.72, 1.053 fixed, 1, 3.567, 2.489, 1.433 fixed, 2, 2.577, 3.649, 0.706 fixed, 3, 3.644, 5.983, 0.609 fixed, 4, 4.211, 6.833, 0.616 fixed, 5, 4.741, 9.372, 0.506 fixed, 6, 5.415, 9.561, 0.566 fixed, 7, 6.649, 10.789, 0.616 fixed, 8, 8.081, 11.808, 0.684 fixed, 9, 8.427, 12.935, 0.651 fixed, 10, 8.673, 14.134, 0.614 fixed, 11, 10.69, 15.408, 0.694 fixed, 12, 10.789, 16.982, 0.635 fixed, 13, 12.169, 18.411, 0.661 fixed, 14, 12.659, 19.914, 0.636 fixed, 15, 13.526, 21.541, 0.628 fixed, 16, 14.211, 23.088, 0.616 fixed, 32, 29.412, 52.722, 0.558 fixed, 64, 65.41, 142.351, 0.459 fixed, 128, 138.505, 295.625, 0.469 fixed, 256, 291.707, 601.983, 0.485 random, 2, 12.698, 12.849, 0.988 random, 4, 16.065, 15.857, 1.013 random, 8, 19.564, 21.105, 0.927 random, 16, 23.919, 26.823, 0.892 random, 32, 31.987, 39.591, 0.808 random, 64, 49.282, 71.487, 0.689 random, 128, 82.23, 145.364, 0.566 random, 256, 152.209, 298.434, 0.51 Co-authored-by: Alexander Monakov <amonakov@ispras.ru> Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
This commit is contained in:
Noah Goldstein
parent
3d155d4b6c
commit
9a421348cd
@ -16,7 +16,8 @@
|
||||
License along with the GNU C Library; if not, see
|
||||
<https://www.gnu.org/licenses/>. */
|
||||
|
||||
#include <elf/dl-new-hash.h>
|
||||
#include <dl-new-hash.h>
|
||||
#include <elf/simple-dl-new-hash.h>
|
||||
#define TEST_FUNC(x, y) _dl_new_hash (x)
|
||||
#define SIMPLE_TEST_FUNC(x, y) __simple_dl_new_hash (x)
|
||||
|
||||
|
||||
@ -1,4 +1,4 @@
|
||||
/* _dl_new_hash for elf symbol lookup
|
||||
/* __simple_dl_new_hash for testing true elf symbol lookup.
|
||||
Copyright (C) 2022 Free Software Foundation, Inc.
|
||||
This file is part of the GNU C Library.
|
||||
|
||||
@ -16,16 +16,16 @@
|
||||
License along with the GNU C Library; if not, see
|
||||
<https://www.gnu.org/licenses/>. */
|
||||
|
||||
#ifndef _DL_NEW_HASH_H
|
||||
#define _DL_NEW_HASH_H 1
|
||||
#ifndef _SIMPLE_DL_NEW_HASH_H
|
||||
#define _SIMPLE_DL_NEW_HASH_H 1
|
||||
|
||||
#include <stdint.h>
|
||||
/* For __always_inline. */
|
||||
#include <sys/cdefs.h>
|
||||
|
||||
static __always_inline uint32_t
|
||||
/* For testing/benchmarking purposes. Real implementation in
|
||||
sysdeps/generic/dl-new-hash.h. */
|
||||
static uint32_t
|
||||
__attribute__ ((unused))
|
||||
_dl_new_hash (const char *s)
|
||||
__simple_dl_new_hash (const char *s)
|
||||
{
|
||||
uint32_t h = 5381;
|
||||
for (unsigned char c = *s; c != '\0'; c = *++s)
|
||||
@ -33,8 +33,4 @@ _dl_new_hash (const char *s)
|
||||
return h;
|
||||
}
|
||||
|
||||
/* For testing/benchmarking purposes. */
|
||||
#define __simple_dl_new_hash _dl_new_hash
|
||||
|
||||
|
||||
#endif /* dl-new-hash.h */
|
||||
#endif /* simple-dl-new-hash.h */
|
||||
@ -18,6 +18,7 @@
|
||||
|
||||
|
||||
#include <simple-dl-hash.h>
|
||||
#include <simple-dl-new-hash.h>
|
||||
#include <dl-hash.h>
|
||||
#include <dl-new-hash.h>
|
||||
#include <support/support.h>
|
||||
|
||||
109
sysdeps/generic/dl-new-hash.h
Normal file
109
sysdeps/generic/dl-new-hash.h
Normal file
@ -0,0 +1,109 @@
|
||||
/* _dl_new_hash for elf symbol lookup
|
||||
Copyright (C) 2022 Free Software Foundation, Inc.
|
||||
This file is part of the GNU C Library.
|
||||
|
||||
The GNU C Library is free software; you can redistribute it and/or
|
||||
modify it under the terms of the GNU Lesser General Public
|
||||
License as published by the Free Software Foundation; either
|
||||
version 2.1 of the License, or (at your option) any later version.
|
||||
|
||||
The GNU C Library is distributed in the hope that it will be useful,
|
||||
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||||
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
||||
Lesser General Public License for more details.
|
||||
|
||||
You should have received a copy of the GNU Lesser General Public
|
||||
License along with the GNU C Library; if not, see
|
||||
<https://www.gnu.org/licenses/>. */
|
||||
|
||||
#ifndef _DL_NEW_HASH_H
|
||||
#define _DL_NEW_HASH_H 1
|
||||
|
||||
#include <stdint.h>
|
||||
/* For __always_inline and __glibc_unlikely. */
|
||||
#include <sys/cdefs.h>
|
||||
|
||||
/* The simplest implementation of _dl_new_hash is:
|
||||
|
||||
_dl_new_hash (const char *s)
|
||||
{
|
||||
uint32_t h = 5381;
|
||||
for (unsigned char c = *s; c != '\0'; c = *++s)
|
||||
h = h * 33 + c;
|
||||
return h;
|
||||
}
|
||||
|
||||
We can get better performance by slightly unrolling the loop to
|
||||
pipeline the multiples, which gcc cannot easily do due to
|
||||
dependencies across iterations.
|
||||
|
||||
As well, as an architecture specific option we add asm statements
|
||||
to explicitly specify order of operations and prevent reassociation
|
||||
of instructions that lengthens the loop carried dependency. This
|
||||
may have no affect as the compiler may have ordered instructions
|
||||
the same way without it but in testing this has not been the case
|
||||
for GCC. Improving GCC to reliably schedule instructions ideally
|
||||
cannot be easily done.
|
||||
|
||||
Architecture(s) that use the reassociation barriers are:
|
||||
x86
|
||||
|
||||
Note it is very unlikely the reassociation barriers would
|
||||
de-optimize performance on any architecture and with an imperfect
|
||||
compiler it may help performance, especially on out-of-order cpus,
|
||||
so it is suggested that the respective maintainers add them.
|
||||
|
||||
Architecture maintainers are encouraged to benchmark this with
|
||||
__asm_reassociation_barrier defined to __asm__ like it is in x86.
|
||||
*/
|
||||
|
||||
|
||||
#ifndef __asm_reassociation_barrier
|
||||
# define __asm_reassociation_barrier(...)
|
||||
#endif
|
||||
|
||||
static __always_inline uint32_t
|
||||
__attribute__ ((unused))
|
||||
_dl_new_hash (const char *str)
|
||||
{
|
||||
const unsigned char *s = (const unsigned char *) str;
|
||||
unsigned int h = 5381;
|
||||
unsigned int c0, c1;
|
||||
for (;;)
|
||||
{
|
||||
c0 = s[0];
|
||||
/* Since hashed string is normally not empty, this is unlikely on the
|
||||
first iteration of the loop. */
|
||||
if (__glibc_unlikely (c0 == 0))
|
||||
return h;
|
||||
|
||||
c1 = s[1];
|
||||
if (c1 == 0)
|
||||
{
|
||||
/* Ideal computational order is:
|
||||
c0 += h;
|
||||
h *= 32;
|
||||
h += c0; */
|
||||
c0 += h;
|
||||
__asm_reassociation_barrier("" : "+r"(h) : "r"(c0));
|
||||
h = h * 32 + c0;
|
||||
return h;
|
||||
}
|
||||
|
||||
/* Ideal computational order is:
|
||||
c1 += c0;
|
||||
h *= 33 * 33;
|
||||
c0 *= 32;
|
||||
c1 += c0;
|
||||
h += c1; */
|
||||
c1 += c0;
|
||||
__asm_reassociation_barrier("" : "+r"(c1), "+r"(c0));
|
||||
h *= 33 * 33;
|
||||
c1 += c0 * 32;
|
||||
__asm_reassociation_barrier("" : "+r"(c1));
|
||||
h += c1;
|
||||
s += 2;
|
||||
}
|
||||
}
|
||||
|
||||
#endif /* dl-new-hash.h */
|
||||
24
sysdeps/x86/dl-new-hash.h
Normal file
24
sysdeps/x86/dl-new-hash.h
Normal file
@ -0,0 +1,24 @@
|
||||
/* _dl_new_hash for elf symbol lookup
|
||||
Copyright (C) 2022 Free Software Foundation, Inc.
|
||||
This file is part of the GNU C Library.
|
||||
|
||||
The GNU C Library is free software; you can redistribute it and/or
|
||||
modify it under the terms of the GNU Lesser General Public
|
||||
License as published by the Free Software Foundation; either
|
||||
version 2.1 of the License, or (at your option) any later version.
|
||||
|
||||
The GNU C Library is distributed in the hope that it will be useful,
|
||||
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||||
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
||||
Lesser General Public License for more details.
|
||||
|
||||
You should have received a copy of the GNU Lesser General Public
|
||||
License along with the GNU C Library; if not, see
|
||||
<https://www.gnu.org/licenses/>. */
|
||||
|
||||
#ifdef __asm_reassociation_barrier
|
||||
# error "__asm_reassociation_barrier should never already be defined."
|
||||
#endif
|
||||
|
||||
#define __asm_reassociation_barrier __asm__
|
||||
#include <sysdeps/generic/dl-new-hash.h>
|
||||
Loading…
Reference in New Issue
Block a user