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Diffstat (limited to 'util/timed-average.c')
| -rw-r--r-- | util/timed-average.c | 210 |
1 files changed, 210 insertions, 0 deletions
diff --git a/util/timed-average.c b/util/timed-average.c new file mode 100644 index 0000000000..98a1170204 --- /dev/null +++ b/util/timed-average.c @@ -0,0 +1,210 @@ +/* + * QEMU timed average computation + * + * Copyright (C) Nodalink, EURL. 2014 + * Copyright (C) Igalia, S.L. 2015 + * + * Authors: + * Benoît Canet <benoit.canet@nodalink.com> + * Alberto Garcia <berto@igalia.com> + * + * This program is free sofware: you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Sofware Foundation, either version 2 of the License, or + * (at your option) version 3 or any later version. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program. If not, see <http://www.gnu.org/licenses/>. + */ + +#include <string.h> + +#include "qemu/timed-average.h" + +/* This module computes an average of a set of values within a time + * window. + * + * Algorithm: + * + * - Create two windows with a certain expiration period, and + * offsetted by period / 2. + * - Each time you want to account a new value, do it in both windows. + * - The minimum / maximum / average values are always returned from + * the oldest window. + * + * Example: + * + * t=0 |t=0.5 |t=1 |t=1.5 |t=2 + * wnd0: [0,0.5)|wnd0: [0.5,1.5) | |wnd0: [1.5,2.5) | + * wnd1: [0,1) | |wnd1: [1,2) | | + * + * Values are returned from: + * + * wnd0---------|wnd1------------|wnd0---------|wnd1-------------| + */ + +/* Update the expiration of a time window + * + * @w: the window used + * @now: the current time in nanoseconds + * @period: the expiration period in nanoseconds + */ +static void update_expiration(TimedAverageWindow *w, int64_t now, + int64_t period) +{ + /* time elapsed since the last theoretical expiration */ + int64_t elapsed = (now - w->expiration) % period; + /* time remaininging until the next expiration */ + int64_t remaining = period - elapsed; + /* compute expiration */ + w->expiration = now + remaining; +} + +/* Reset a window + * + * @w: the window to reset + */ +static void window_reset(TimedAverageWindow *w) +{ + w->min = UINT64_MAX; + w->max = 0; + w->sum = 0; + w->count = 0; +} + +/* Get the current window (that is, the one with the earliest + * expiration time). + * + * @ta: the TimedAverage structure + * @ret: a pointer to the current window + */ +static TimedAverageWindow *current_window(TimedAverage *ta) +{ + return &ta->windows[ta->current]; +} + +/* Initialize a TimedAverage structure + * + * @ta: the TimedAverage structure + * @clock_type: the type of clock to use + * @period: the time window period in nanoseconds + */ +void timed_average_init(TimedAverage *ta, QEMUClockType clock_type, + uint64_t period) +{ + int64_t now = qemu_clock_get_ns(clock_type); + + /* Returned values are from the oldest window, so they belong to + * the interval [ta->period/2,ta->period). By adjusting the + * requested period by 4/3, we guarantee that they're in the + * interval [2/3 period,4/3 period), closer to the requested + * period on average */ + ta->period = (uint64_t) period * 4 / 3; + ta->clock_type = clock_type; + ta->current = 0; + + window_reset(&ta->windows[0]); + window_reset(&ta->windows[1]); + + /* Both windows are offsetted by half a period */ + ta->windows[0].expiration = now + ta->period / 2; + ta->windows[1].expiration = now + ta->period; +} + +/* Check if the time windows have expired, updating their counters and + * expiration time if that's the case. + * + * @ta: the TimedAverage structure + */ +static void check_expirations(TimedAverage *ta) +{ + int64_t now = qemu_clock_get_ns(ta->clock_type); + int i; + + assert(ta->period != 0); + + /* Check if the windows have expired */ + for (i = 0; i < 2; i++) { + TimedAverageWindow *w = &ta->windows[i]; + if (w->expiration <= now) { + window_reset(w); + update_expiration(w, now, ta->period); + } + } + + /* Make ta->current point to the oldest window */ + if (ta->windows[0].expiration < ta->windows[1].expiration) { + ta->current = 0; + } else { + ta->current = 1; + } +} + +/* Account a value + * + * @ta: the TimedAverage structure + * @value: the value to account + */ +void timed_average_account(TimedAverage *ta, uint64_t value) +{ + int i; + check_expirations(ta); + + /* Do the accounting in both windows at the same time */ + for (i = 0; i < 2; i++) { + TimedAverageWindow *w = &ta->windows[i]; + + w->sum += value; + w->count++; + + if (value < w->min) { + w->min = value; + } + + if (value > w->max) { + w->max = value; + } + } +} + +/* Get the minimum value + * + * @ta: the TimedAverage structure + * @ret: the minimum value + */ +uint64_t timed_average_min(TimedAverage *ta) +{ + TimedAverageWindow *w; + check_expirations(ta); + w = current_window(ta); + return w->min < UINT64_MAX ? w->min : 0; +} + +/* Get the average value + * + * @ta: the TimedAverage structure + * @ret: the average value + */ +uint64_t timed_average_avg(TimedAverage *ta) +{ + TimedAverageWindow *w; + check_expirations(ta); + w = current_window(ta); + return w->count > 0 ? w->sum / w->count : 0; +} + +/* Get the maximum value + * + * @ta: the TimedAverage structure + * @ret: the maximum value + */ +uint64_t timed_average_max(TimedAverage *ta) +{ + check_expirations(ta); + return current_window(ta)->max; +} |