util: Infrastructure for computing recent averages

This module computes the average of a set of values within a time
window, keeping also track of the minimum and maximum values.

In order to produce more accurate results it works internally by
creating two time windows of the same period, offsetted by half of
that period. Values are accounted on both windows and the data is
always returned from the oldest one.

[Add missing util/replay.o to test-timed-average dependencies to fix the
build.
--Stefan]

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id: 201b09c21bbc9c329779d2b2365ee2b9c80dceeb.1446044837.git.berto@igalia.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 63 insertions, 0 deletions

diff --git a/include/qemu/timed-average.h b/include/qemu/timed-average.h
new file mode 100644
index 0000000000..f1cdddc48b
--- /dev/null
+++ b/include/qemu/timed-average.h
@@ -0,0 +1,63 @@
+/*
+ * 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 software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software 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/>.
+ */
+
+#ifndef TIMED_AVERAGE_H
+#define TIMED_AVERAGE_H
+
+#include <stdint.h>
+
+#include "qemu/timer.h"
+
+typedef struct TimedAverageWindow TimedAverageWindow;
+typedef struct TimedAverage TimedAverage;
+
+/* All fields of both structures are private */
+
+struct TimedAverageWindow {
+    uint64_t      min;             /* minimum value accounted in the window */
+    uint64_t      max;             /* maximum value accounted in the window */
+    uint64_t      sum;             /* sum of all values */
+    uint64_t      count;           /* number of values */
+    int64_t       expiration;      /* the end of the current window in ns */
+};
+
+struct TimedAverage {
+    uint64_t           period;     /* period in nanoseconds */
+    TimedAverageWindow windows[2]; /* two overlapping windows of with
+                                    * an offset of period / 2 between them */
+    unsigned           current;    /* the current window index: it's also the
+                                    * oldest window index */
+    QEMUClockType      clock_type; /* the clock used */
+};
+
+void timed_average_init(TimedAverage *ta, QEMUClockType clock_type,
+                        uint64_t period);
+
+void timed_average_account(TimedAverage *ta, uint64_t value);
+
+uint64_t timed_average_min(TimedAverage *ta);
+uint64_t timed_average_avg(TimedAverage *ta);
+uint64_t timed_average_max(TimedAverage *ta);
+
+#endif