--- /dev/null
+/*
+ * 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 "qemu/osdep.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
+ * @elapsed: if non-NULL, the elapsed time (in ns) within the current
+ * window will be stored here
+ */
+static void check_expirations(TimedAverage *ta, uint64_t *elapsed)
+{
+ 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;
+ }
+
+ /* Calculate the elapsed time within the current window */
+ if (elapsed) {
+ int64_t remaining = ta->windows[ta->current].expiration - now;
+ *elapsed = ta->period - remaining;
+ }
+}
+
+/* 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, NULL);
+
+ /* 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, NULL);
+ 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, NULL);
+ 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, NULL);
+ return current_window(ta)->max;
+}
+
+/* Get the sum of all accounted values
+ * @ta: the TimedAverage structure
+ * @elapsed: if non-NULL, the elapsed time (in ns) will be stored here
+ * @ret: the sum of all accounted values
+ */
+uint64_t timed_average_sum(TimedAverage *ta, uint64_t *elapsed)
+{
+ TimedAverageWindow *w;
+ check_expirations(ta, elapsed);
+ w = current_window(ta);
+ return w->sum;
+}
Code Review / kvmfornfv.git / blobdiff