linux/lib/find_bit_benchmark.c
Yury Norov f68edc9297 lib: add find_first_and_bit()
Currently find_first_and_bit() is an alias to find_next_and_bit(). However,
it is widely used in cpumask, so it worth to optimize it. This patch adds
its own implementation for find_first_and_bit().

On x86_64 find_bit_benchmark says:

Before (#define find_first_and_bit(...) find_next_and_bit(..., 0):
Start testing find_bit() with random-filled bitmap
[  140.291468] find_first_and_bit:           46890919 ns,  32671 iterations
Start testing find_bit() with sparse bitmap
[  140.295028] find_first_and_bit:               7103 ns,      1 iterations

After:
Start testing find_bit() with random-filled bitmap
[  162.574907] find_first_and_bit:           25045813 ns,  32846 iterations
Start testing find_bit() with sparse bitmap
[  162.578458] find_first_and_bit:               4900 ns,      1 iterations

(Thanks to Alexey Klimov for thorough testing.)

Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Alexey Klimov <aklimov@redhat.com>
2022-01-15 08:47:31 -08:00

180 lines
4.5 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Test for find_*_bit functions.
*
* Copyright (c) 2017 Cavium.
*/
/*
* find_bit functions are widely used in kernel, so the successful boot
* is good enough test for correctness.
*
* This test is focused on performance of traversing bitmaps. Two typical
* scenarios are reproduced:
* - randomly filled bitmap with approximately equal number of set and
* cleared bits;
* - sparse bitmap with few set bits at random positions.
*/
#include <linux/bitops.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/random.h>
#define BITMAP_LEN (4096UL * 8 * 10)
#define SPARSE 500
static DECLARE_BITMAP(bitmap, BITMAP_LEN) __initdata;
static DECLARE_BITMAP(bitmap2, BITMAP_LEN) __initdata;
/*
* This is Schlemiel the Painter's algorithm. It should be called after
* all other tests for the same bitmap because it sets all bits of bitmap to 1.
*/
static int __init test_find_first_bit(void *bitmap, unsigned long len)
{
unsigned long i, cnt;
ktime_t time;
time = ktime_get();
for (cnt = i = 0; i < len; cnt++) {
i = find_first_bit(bitmap, len);
__clear_bit(i, bitmap);
}
time = ktime_get() - time;
pr_err("find_first_bit: %18llu ns, %6ld iterations\n", time, cnt);
return 0;
}
static int __init test_find_first_and_bit(void *bitmap, const void *bitmap2, unsigned long len)
{
static DECLARE_BITMAP(cp, BITMAP_LEN) __initdata;
unsigned long i, cnt;
ktime_t time;
bitmap_copy(cp, bitmap, BITMAP_LEN);
time = ktime_get();
for (cnt = i = 0; i < len; cnt++) {
i = find_first_and_bit(cp, bitmap2, len);
__clear_bit(i, cp);
}
time = ktime_get() - time;
pr_err("find_first_and_bit: %18llu ns, %6ld iterations\n", time, cnt);
return 0;
}
static int __init test_find_next_bit(const void *bitmap, unsigned long len)
{
unsigned long i, cnt;
ktime_t time;
time = ktime_get();
for (cnt = i = 0; i < BITMAP_LEN; cnt++)
i = find_next_bit(bitmap, BITMAP_LEN, i) + 1;
time = ktime_get() - time;
pr_err("find_next_bit: %18llu ns, %6ld iterations\n", time, cnt);
return 0;
}
static int __init test_find_next_zero_bit(const void *bitmap, unsigned long len)
{
unsigned long i, cnt;
ktime_t time;
time = ktime_get();
for (cnt = i = 0; i < BITMAP_LEN; cnt++)
i = find_next_zero_bit(bitmap, len, i) + 1;
time = ktime_get() - time;
pr_err("find_next_zero_bit: %18llu ns, %6ld iterations\n", time, cnt);
return 0;
}
static int __init test_find_last_bit(const void *bitmap, unsigned long len)
{
unsigned long l, cnt = 0;
ktime_t time;
time = ktime_get();
do {
cnt++;
l = find_last_bit(bitmap, len);
if (l >= len)
break;
len = l;
} while (len);
time = ktime_get() - time;
pr_err("find_last_bit: %18llu ns, %6ld iterations\n", time, cnt);
return 0;
}
static int __init test_find_next_and_bit(const void *bitmap,
const void *bitmap2, unsigned long len)
{
unsigned long i, cnt;
ktime_t time;
time = ktime_get();
for (cnt = i = 0; i < BITMAP_LEN; cnt++)
i = find_next_and_bit(bitmap, bitmap2, BITMAP_LEN, i + 1);
time = ktime_get() - time;
pr_err("find_next_and_bit: %18llu ns, %6ld iterations\n", time, cnt);
return 0;
}
static int __init find_bit_test(void)
{
unsigned long nbits = BITMAP_LEN / SPARSE;
pr_err("\nStart testing find_bit() with random-filled bitmap\n");
get_random_bytes(bitmap, sizeof(bitmap));
get_random_bytes(bitmap2, sizeof(bitmap2));
test_find_next_bit(bitmap, BITMAP_LEN);
test_find_next_zero_bit(bitmap, BITMAP_LEN);
test_find_last_bit(bitmap, BITMAP_LEN);
/*
* test_find_first_bit() may take some time, so
* traverse only part of bitmap to avoid soft lockup.
*/
test_find_first_bit(bitmap, BITMAP_LEN / 10);
test_find_first_and_bit(bitmap, bitmap2, BITMAP_LEN / 2);
test_find_next_and_bit(bitmap, bitmap2, BITMAP_LEN);
pr_err("\nStart testing find_bit() with sparse bitmap\n");
bitmap_zero(bitmap, BITMAP_LEN);
bitmap_zero(bitmap2, BITMAP_LEN);
while (nbits--) {
__set_bit(prandom_u32() % BITMAP_LEN, bitmap);
__set_bit(prandom_u32() % BITMAP_LEN, bitmap2);
}
test_find_next_bit(bitmap, BITMAP_LEN);
test_find_next_zero_bit(bitmap, BITMAP_LEN);
test_find_last_bit(bitmap, BITMAP_LEN);
test_find_first_bit(bitmap, BITMAP_LEN);
test_find_first_and_bit(bitmap, bitmap2, BITMAP_LEN);
test_find_next_and_bit(bitmap, bitmap2, BITMAP_LEN);
/*
* Everything is OK. Return error just to let user run benchmark
* again without annoying rmmod.
*/
return -EINVAL;
}
module_init(find_bit_test);
MODULE_LICENSE("GPL");