LXR linux/lib/find_bit

   1/*
   2 * Test for find_*_bit functions.
   3 *
   4 * Copyright (c) 2017 Cavium.
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of version 2 of the GNU General Public
   8 * License as published by the Free Software Foundation.
   9 *
  10 * This program is distributed in the hope that it will be useful, but
  11 * WITHOUT ANY WARRANTY; without even the implied warranty of
  12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  13 * General Public License for more details.
  14 */
  15
  16/*
  17 * find_bit functions are widely used in kernel, so the successful boot
  18 * is good enough test for correctness.
  19 *
  20 * This test is focused on performance of traversing bitmaps. Two typical
  21 * scenarios are reproduced:
  22 * - randomly filled bitmap with approximately equal number of set and
  23 *   cleared bits;
  24 * - sparse bitmap with few set bits at random positions.
  25 */
  26
  27#include <linux/bitops.h>
  28#include <linux/kernel.h>
  29#include <linux/list.h>
  30#include <linux/module.h>
  31#include <linux/printk.h>
  32#include <linux/random.h>
  33
  34#define BITMAP_LEN      (4096UL * 8 * 10)
  35#define SPARSE          500
  36
  37static DECLARE_BITMAP(bitmap, BITMAP_LEN) __initdata;
  38static DECLARE_BITMAP(bitmap2, BITMAP_LEN) __initdata;
  39
  40/*
  41 * This is Schlemiel the Painter's algorithm. It should be called after
  42 * all other tests for the same bitmap because it sets all bits of bitmap to 1.
  43 */
  44static int __init test_find_first_bit(void *bitmap, unsigned long len)
  45{
  46        unsigned long i, cnt;
  47        ktime_t time;
  48
  49        time = ktime_get();
  50        for (cnt = i = 0; i < len; cnt++) {
  51                i = find_first_bit(bitmap, len);
  52                __clear_bit(i, bitmap);
  53        }
  54        time = ktime_get() - time;
  55        pr_err("find_first_bit:     %18llu ns, %6ld iterations\n", time, cnt);
  56
  57        return 0;
  58}
  59
  60static int __init test_find_next_bit(const void *bitmap, unsigned long len)
  61{
  62        unsigned long i, cnt;
  63        ktime_t time;
  64
  65        time = ktime_get();
  66        for (cnt = i = 0; i < BITMAP_LEN; cnt++)
  67                i = find_next_bit(bitmap, BITMAP_LEN, i) + 1;
  68        time = ktime_get() - time;
  69        pr_err("find_next_bit:      %18llu ns, %6ld iterations\n", time, cnt);
  70
  71        return 0;
  72}
  73
  74static int __init test_find_next_zero_bit(const void *bitmap, unsigned long len)
  75{
  76        unsigned long i, cnt;
  77        ktime_t time;
  78
  79        time = ktime_get();
  80        for (cnt = i = 0; i < BITMAP_LEN; cnt++)
  81                i = find_next_zero_bit(bitmap, len, i) + 1;
  82        time = ktime_get() - time;
  83        pr_err("find_next_zero_bit: %18llu ns, %6ld iterations\n", time, cnt);
  84
  85        return 0;
  86}
  87
  88static int __init test_find_last_bit(const void *bitmap, unsigned long len)
  89{
  90        unsigned long l, cnt = 0;
  91        ktime_t time;
  92
  93        time = ktime_get();
  94        do {
  95                cnt++;
  96                l = find_last_bit(bitmap, len);
  97                if (l >= len)
  98                        break;
  99                len = l;
 100        } while (len);
 101        time = ktime_get() - time;
 102        pr_err("find_last_bit:      %18llu ns, %6ld iterations\n", time, cnt);
 103
 104        return 0;
 105}
 106
 107static int __init test_find_next_and_bit(const void *bitmap,
 108                const void *bitmap2, unsigned long len)
 109{
 110        unsigned long i, cnt;
 111        cycles_t cycles;
 112
 113        cycles = get_cycles();
 114        for (cnt = i = 0; i < BITMAP_LEN; cnt++)
 115                i = find_next_and_bit(bitmap, bitmap2, BITMAP_LEN, i+1);
 116        cycles = get_cycles() - cycles;
 117        pr_err("find_next_and_bit:\t\t%llu cycles, %ld iterations\n",
 118                (u64)cycles, cnt);
 119
 120        return 0;
 121}
 122
 123static int __init find_bit_test(void)
 124{
 125        unsigned long nbits = BITMAP_LEN / SPARSE;
 126
 127        pr_err("\nStart testing find_bit() with random-filled bitmap\n");
 128
 129        get_random_bytes(bitmap, sizeof(bitmap));
 130        get_random_bytes(bitmap2, sizeof(bitmap2));
 131
 132        test_find_next_bit(bitmap, BITMAP_LEN);
 133        test_find_next_zero_bit(bitmap, BITMAP_LEN);
 134        test_find_last_bit(bitmap, BITMAP_LEN);
 135
 136        /*
 137         * test_find_first_bit() may take some time, so
 138         * traverse only part of bitmap to avoid soft lockup.
 139         */
 140        test_find_first_bit(bitmap, BITMAP_LEN / 10);
 141        test_find_next_and_bit(bitmap, bitmap2, BITMAP_LEN);
 142
 143        pr_err("\nStart testing find_bit() with sparse bitmap\n");
 144
 145        bitmap_zero(bitmap, BITMAP_LEN);
 146        bitmap_zero(bitmap2, BITMAP_LEN);
 147
 148        while (nbits--) {
 149                __set_bit(prandom_u32() % BITMAP_LEN, bitmap);
 150                __set_bit(prandom_u32() % BITMAP_LEN, bitmap2);
 151        }
 152
 153        test_find_next_bit(bitmap, BITMAP_LEN);
 154        test_find_next_zero_bit(bitmap, BITMAP_LEN);
 155        test_find_last_bit(bitmap, BITMAP_LEN);
 156        test_find_first_bit(bitmap, BITMAP_LEN);
 157        test_find_next_and_bit(bitmap, bitmap2, BITMAP_LEN);
 158
 159        /*
 160         * Everything is OK. Return error just to let user run benchmark
 161         * again without annoying rmmod.
 162         */
 163        return -EINVAL;
 164}
 165module_init(find_bit_test);
 166
 167MODULE_LICENSE("GPL");
 168