| 1 | /* |
| 2 | * QEMU timed average computation |
| 3 | * |
| 4 | * Copyright (C) Nodalink, EURL. 2014 |
| 5 | * Copyright (C) Igalia, S.L. 2015 |
| 6 | * |
| 7 | * Authors: |
| 8 | * Benoît Canet <benoit.canet@nodalink.com> |
| 9 | * Alberto Garcia <berto@igalia.com> |
| 10 | * |
| 11 | * SPDX-License-Identifier: GPL-2.0-or-later |
| 12 | * |
| 13 | * This program is free software: you can redistribute it and/or modify |
| 14 | * it under the terms of the GNU General Public License as published by |
| 15 | * the Free Software Foundation, either version 2 of the License, or |
| 16 | * (at your option) any later version. |
| 17 | * |
| 18 | * This program is distributed in the hope that it will be useful, |
| 19 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 20 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 21 | * GNU General Public License for more details. |
| 22 | * |
| 23 | * You should have received a copy of the GNU General Public License |
| 24 | * along with this program. If not, see <http://www.gnu.org/licenses/>. |
| 25 | */ |
| 26 | |
| 27 | #include "qemu/osdep.h" |
| 28 | |
| 29 | #include "qemu/timed-average.h" |
| 30 | |
| 31 | /* This module computes an average of a set of values within a time |
| 32 | * window. |
| 33 | * |
| 34 | * Algorithm: |
| 35 | * |
| 36 | * - Create two windows with a certain expiration period, and |
| 37 | * offsetted by period / 2. |
| 38 | * - Each time you want to account a new value, do it in both windows. |
| 39 | * - The minimum / maximum / average values are always returned from |
| 40 | * the oldest window. |
| 41 | * |
| 42 | * Example: |
| 43 | * |
| 44 | * t=0 |t=0.5 |t=1 |t=1.5 |t=2 |
| 45 | * wnd0: [0,0.5)|wnd0: [0.5,1.5) | |wnd0: [1.5,2.5) | |
| 46 | * wnd1: [0,1) | |wnd1: [1,2) | | |
| 47 | * |
| 48 | * Values are returned from: |
| 49 | * |
| 50 | * wnd0---------|wnd1------------|wnd0---------|wnd1-------------| |
| 51 | */ |
| 52 | |
| 53 | /* Update the expiration of a time window |
| 54 | * |
| 55 | * @w: the window used |
| 56 | * @now: the current time in nanoseconds |
| 57 | * @period: the expiration period in nanoseconds |
| 58 | */ |
| 59 | static void update_expiration(TimedAverageWindow *w, int64_t now, |
| 60 | int64_t period) |
| 61 | { |
| 62 | /* time elapsed since the last theoretical expiration */ |
| 63 | int64_t elapsed = (now - w->expiration) % period; |
| 64 | /* time remaininging until the next expiration */ |
| 65 | int64_t remaining = period - elapsed; |
| 66 | /* compute expiration */ |
| 67 | w->expiration = now + remaining; |
| 68 | } |
| 69 | |
| 70 | /* Reset a window |
| 71 | * |
| 72 | * @w: the window to reset |
| 73 | */ |
| 74 | static void window_reset(TimedAverageWindow *w) |
| 75 | { |
| 76 | w->min = UINT64_MAX; |
| 77 | w->max = 0; |
| 78 | w->sum = 0; |
| 79 | w->count = 0; |
| 80 | } |
| 81 | |
| 82 | /* Get the current window (that is, the one with the earliest |
| 83 | * expiration time). |
| 84 | * |
| 85 | * @ta: the TimedAverage structure |
| 86 | * @ret: a pointer to the current window |
| 87 | */ |
| 88 | static TimedAverageWindow *current_window(TimedAverage *ta) |
| 89 | { |
| 90 | return &ta->windows[ta->current]; |
| 91 | } |
| 92 | |
| 93 | /* Initialize a TimedAverage structure |
| 94 | * |
| 95 | * @ta: the TimedAverage structure |
| 96 | * @clock_type: the type of clock to use |
| 97 | * @period: the time window period in nanoseconds |
| 98 | */ |
| 99 | void timed_average_init(TimedAverage *ta, QEMUClockType clock_type, |
| 100 | uint64_t period) |
| 101 | { |
| 102 | int64_t now = qemu_clock_get_ns(clock_type); |
| 103 | |
| 104 | /* Returned values are from the oldest window, so they belong to |
| 105 | * the interval [ta->period/2,ta->period). By adjusting the |
| 106 | * requested period by 4/3, we guarantee that they're in the |
| 107 | * interval [2/3 period,4/3 period), closer to the requested |
| 108 | * period on average */ |
| 109 | ta->period = (uint64_t) period * 4 / 3; |
| 110 | ta->clock_type = clock_type; |
| 111 | ta->current = 0; |
| 112 | |
| 113 | window_reset(&ta->windows[0]); |
| 114 | window_reset(&ta->windows[1]); |
| 115 | |
| 116 | /* Both windows are offsetted by half a period */ |
| 117 | ta->windows[0].expiration = now + ta->period / 2; |
| 118 | ta->windows[1].expiration = now + ta->period; |
| 119 | } |
| 120 | |
| 121 | /* Check if the time windows have expired, updating their counters and |
| 122 | * expiration time if that's the case. |
| 123 | * |
| 124 | * @ta: the TimedAverage structure |
| 125 | * @elapsed: if non-NULL, the elapsed time (in ns) within the current |
| 126 | * window will be stored here |
| 127 | */ |
| 128 | static void check_expirations(TimedAverage *ta, uint64_t *elapsed) |
| 129 | { |
| 130 | int64_t now = qemu_clock_get_ns(ta->clock_type); |
| 131 | int i; |
| 132 | |
| 133 | assert(ta->period != 0); |
| 134 | |
| 135 | /* Check if the windows have expired */ |
| 136 | for (i = 0; i < 2; i++) { |
| 137 | TimedAverageWindow *w = &ta->windows[i]; |
| 138 | if (w->expiration <= now) { |
| 139 | window_reset(w); |
| 140 | update_expiration(w, now, ta->period); |
| 141 | } |
| 142 | } |
| 143 | |
| 144 | /* Make ta->current point to the oldest window */ |
| 145 | if (ta->windows[0].expiration < ta->windows[1].expiration) { |
| 146 | ta->current = 0; |
| 147 | } else { |
| 148 | ta->current = 1; |
| 149 | } |
| 150 | |
| 151 | /* Calculate the elapsed time within the current window */ |
| 152 | if (elapsed) { |
| 153 | int64_t remaining = ta->windows[ta->current].expiration - now; |
| 154 | *elapsed = ta->period - remaining; |
| 155 | } |
| 156 | } |
| 157 | |
| 158 | /* Account a value |
| 159 | * |
| 160 | * @ta: the TimedAverage structure |
| 161 | * @value: the value to account |
| 162 | */ |
| 163 | void timed_average_account(TimedAverage *ta, uint64_t value) |
| 164 | { |
| 165 | int i; |
| 166 | check_expirations(ta, NULL); |
| 167 | |
| 168 | /* Do the accounting in both windows at the same time */ |
| 169 | for (i = 0; i < 2; i++) { |
| 170 | TimedAverageWindow *w = &ta->windows[i]; |
| 171 | |
| 172 | w->sum += value; |
| 173 | w->count++; |
| 174 | |
| 175 | if (value < w->min) { |
| 176 | w->min = value; |
| 177 | } |
| 178 | |
| 179 | if (value > w->max) { |
| 180 | w->max = value; |
| 181 | } |
| 182 | } |
| 183 | } |
| 184 | |
| 185 | /* Get the minimum value |
| 186 | * |
| 187 | * @ta: the TimedAverage structure |
| 188 | * @ret: the minimum value |
| 189 | */ |
| 190 | uint64_t timed_average_min(TimedAverage *ta) |
| 191 | { |
| 192 | TimedAverageWindow *w; |
| 193 | check_expirations(ta, NULL); |
| 194 | w = current_window(ta); |
| 195 | return w->min < UINT64_MAX ? w->min : 0; |
| 196 | } |
| 197 | |
| 198 | /* Get the average value |
| 199 | * |
| 200 | * @ta: the TimedAverage structure |
| 201 | * @ret: the average value |
| 202 | */ |
| 203 | uint64_t timed_average_avg(TimedAverage *ta) |
| 204 | { |
| 205 | TimedAverageWindow *w; |
| 206 | check_expirations(ta, NULL); |
| 207 | w = current_window(ta); |
| 208 | return w->count > 0 ? w->sum / w->count : 0; |
| 209 | } |
| 210 | |
| 211 | /* Get the maximum value |
| 212 | * |
| 213 | * @ta: the TimedAverage structure |
| 214 | * @ret: the maximum value |
| 215 | */ |
| 216 | uint64_t timed_average_max(TimedAverage *ta) |
| 217 | { |
| 218 | check_expirations(ta, NULL); |
| 219 | return current_window(ta)->max; |
| 220 | } |
| 221 | |
| 222 | /* Get the sum of all accounted values |
| 223 | * @ta: the TimedAverage structure |
| 224 | * @elapsed: if non-NULL, the elapsed time (in ns) will be stored here |
| 225 | * @ret: the sum of all accounted values |
| 226 | */ |
| 227 | uint64_t timed_average_sum(TimedAverage *ta, uint64_t *elapsed) |
| 228 | { |
| 229 | TimedAverageWindow *w; |
| 230 | check_expirations(ta, elapsed); |
| 231 | w = current_window(ta); |
| 232 | return w->sum; |
| 233 | } |