--- /dev/null
+/*
+ * A program to simulate various queue-drop strategies, using real frame
+ * arrival data as input. Contains various anchors, as well as parametrized
+ * values of the real algorithms that have been used in Nageru over time.
+ *
+ * Expects a log of frame arrivals (in and out). This isn't included in the
+ * git repository because it's quite large, but there's one available
+ * in compressed form at
+ *
+ * https://storage.sesse.net/nageru-latency-log.txt.xz
+ *
+ * The data set in question contains a rather difficult case, with two 50 Hz
+ * clocks slowly drifting from each other (at the rate of about a frame an hour).
+ * This means they are very nearly in sync for a long time, where rare bursts
+ * of jitter can make it hard for the algorithm to find the right level of
+ * conservatism.
+ *
+ * This is not meant to be production-quality code.
+ */
+
+#include <assert.h>
+#include <getopt.h>
+#include <math.h>
+#include <stdio.h>
+#include <locale.h>
+#include <string.h>
+#include <stdlib.h>
+#include <algorithm>
+#include <vector>
+#include <deque>
+#include <memory>
+#include <string>
+#include <limits>
+
+using namespace std;
+
+size_t max_drops = numeric_limits<size_t>::max();
+size_t max_underruns = numeric_limits<size_t>::max();
+double max_latency_ms = numeric_limits<double>::max();
+
+struct Event {
+ enum { IN, OUT } direction;
+ double t;
+};
+
+class Queue {
+public:
+ void add_frame(double t);
+ void get_frame(double now);
+ void drop_frame();
+ void eval(const string &name);
+ size_t queue_len() const { return frames_in_queue.size(); }
+ bool should_abort() const { return num_underruns > max_underruns || num_drops > max_drops; }
+
+private:
+ deque<double> frames_in_queue;
+ size_t num_underruns = 0;
+ size_t num_drops = 0;
+ size_t frames_since_underrun = 0;
+ size_t num_drops_on_first = 0;
+
+ double latency_sum = 0.0;
+ size_t latency_count = 0;
+};
+
+void Queue::add_frame(double t)
+{
+ frames_in_queue.push_back(t);
+}
+
+void Queue::get_frame(double now)
+{
+ if (frames_in_queue.empty()) {
+ ++num_underruns;
+ frames_since_underrun = 0;
+ return;
+ }
+ double t = frames_in_queue.front();
+ frames_in_queue.pop_front();
+ assert(now >= t);
+ latency_sum += (now - t);
+ ++latency_count;
+ ++frames_since_underrun;
+}
+
+void Queue::drop_frame()
+{
+ assert(!frames_in_queue.empty());
+ frames_in_queue.pop_front();
+ ++num_drops;
+ if (frames_since_underrun <= 1) {
+ ++num_drops_on_first;
+ }
+}
+
+void Queue::eval(const string &name)
+{
+ double latency_ms = 1e3 * latency_sum / latency_count;
+ if (num_underruns > max_underruns) return;
+ if (num_drops > max_drops) return;
+ if (latency_ms > max_latency_ms) return;
+ printf("%-50s: %2lu frames left in queue at end, %5lu underruns, %5lu drops (%5lu immediate), %6.2f ms avg latency\n",
+ name.c_str(), frames_in_queue.size(), num_underruns, num_drops, num_drops_on_first, latency_ms);
+}
+
+// A strategy that never drops; low anchor for drops and underruns, high anchor for latency.
+void test_nodrop(const vector<Event> &events)
+{
+ Queue q;
+ for (const Event &event : events) {
+ if (event.direction == Event::IN) {
+ q.add_frame(event.t);
+ } else {
+ q.get_frame(event.t);
+ }
+ }
+ q.eval("no-drop");
+}
+
+// A strategy that accepts only one element in the queue; low anchor for latency.
+void test_limit_to_1(const vector<Event> &events)
+{
+ Queue q;
+ for (const Event &event : events) {
+ if (event.direction == Event::IN) {
+ q.add_frame(event.t);
+ while (q.queue_len() > 1) q.drop_frame();
+ } else {
+ q.get_frame(event.t);
+ }
+ }
+ q.eval("limit-to-1");
+}
+
+// A strategy that accepts one or two elements in the queue.
+void test_limit_to_2(const vector<Event> &events)
+{
+ Queue q;
+ for (const Event &event : events) {
+ if (event.direction == Event::IN) {
+ q.add_frame(event.t);
+ while (q.queue_len() > 2) q.drop_frame();
+ } else {
+ q.get_frame(event.t);
+ }
+ }
+ q.eval("limit-to-2");
+}
+
+// The algorithm used from Nageru 1.2.0 to 1.6.0; raise the ceiling by 1 every time
+// we underrun, drop it if the ceiling hasn't been needed for 1000 frames.
+void test_nageru_1_2_0(const vector<Event> &events)
+{
+ Queue q;
+ unsigned safe_queue_length = 1;
+ unsigned frames_with_at_least_one = 0;
+ bool been_at_safe_point_since_last_starvation = false;
+ for (const Event &event : events) {
+ if (event.direction == Event::IN) {
+ q.add_frame(event.t);
+ } else {
+ unsigned queue_length = q.queue_len();
+ if (queue_length == 0) { // Starvation.
+ if (been_at_safe_point_since_last_starvation /*&& safe_queue_length < unsigned(global_flags.max_input_queue_frames)*/) {
+ ++safe_queue_length;
+ }
+ frames_with_at_least_one = 0;
+ been_at_safe_point_since_last_starvation = false;
+ q.get_frame(event.t); // mark it
+ continue;
+ }
+ if (queue_length >= safe_queue_length) {
+ been_at_safe_point_since_last_starvation = true;
+ }
+ if (++frames_with_at_least_one >= 1000 && safe_queue_length > 1) {
+ --safe_queue_length;
+ frames_with_at_least_one = 0;
+ }
+ while (q.queue_len() > safe_queue_length) {
+ q.drop_frame();
+ }
+ q.get_frame(event.t);
+ }
+ }
+ q.eval("nageru-1.2.0");
+}
+
+class Jitter {
+ const double multiplier, alpha;
+ double expected_timestamp = -1.0;
+ double max_jitter_seconds = 0.0;
+
+public:
+ Jitter(double multiplier, double alpha)
+ : multiplier(multiplier), alpha(alpha) {}
+
+ void update(double timestamp, double frame_duration, size_t dropped_frames)
+ {
+ if (expected_timestamp >= 0.0) {
+ expected_timestamp += dropped_frames * frame_duration;
+ double jitter_seconds = fabs(expected_timestamp - timestamp);
+ max_jitter_seconds = max(multiplier * jitter_seconds, alpha * max_jitter_seconds); // About two seconds half-time.
+
+ // Cap at 100 ms.
+ max_jitter_seconds = min(max_jitter_seconds, 0.1);
+ }
+ expected_timestamp = timestamp + frame_duration;
+ }
+
+ double get_expected() const
+ {
+ return expected_timestamp;
+ }
+
+ double get_jitter() const
+ {
+ return max_jitter_seconds;
+ }
+};
+
+// Keep a running estimate of k times max jitter seen, decreasing by a factor alpha every frame.
+void test_jitter_filter(const vector<Event> &events, double multiplier, double alpha, double margin)
+{
+ Queue q;
+ Jitter input_jitter(multiplier, alpha);
+ Jitter output_jitter(multiplier, alpha);
+
+ for (const Event &event : events) {
+ if (event.direction == Event::IN) {
+ input_jitter.update(event.t, 0.020, 0);
+ q.add_frame(event.t);
+ } else {
+ double now = event.t;
+ output_jitter.update(event.t, 0.020, 0);
+ q.get_frame(event.t);
+
+ double seconds_until_next_frame = max(input_jitter.get_expected() - now + input_jitter.get_jitter(), 0.0);
+ double master_frame_length_seconds = 0.020;
+
+ seconds_until_next_frame += margin; // Hack.
+
+ size_t safe_queue_length = max<int>(floor((seconds_until_next_frame + output_jitter.get_jitter()) / master_frame_length_seconds), 0);
+ while (q.queue_len() > safe_queue_length) {
+ q.drop_frame();
+ }
+ }
+ if (q.should_abort()) return;
+ }
+
+ char name[256];
+ snprintf(name, sizeof(name), "jitter-filter[mul=%.1f,alpha=%.4f,margin=%.1f]", multiplier, alpha, 1e3 * margin);
+ q.eval(name);
+}
+
+// Implements an unbalanced binary search tree that can also satisfy order queries
+// (e.g. “give me the 86th largest entry”).
+class HistoryJitter {
+ const size_t history_length;
+ const double multiplier, percentile;
+ double expected_timestamp = 0.0;
+ double max_jitter_seconds = 0.0;
+ size_t num_updates = 0;
+
+ deque<double> history;
+ struct TreeNode {
+ double val;
+ size_t children = 0;
+ unique_ptr<TreeNode> left, right;
+ };
+ unique_ptr<TreeNode> root;
+
+ unique_ptr<TreeNode> alloc_cache; // Holds the last freed value, for fast reallocation.
+
+ TreeNode *alloc_node()
+ {
+ if (alloc_cache == nullptr) {
+ return new TreeNode;
+ }
+ alloc_cache->children = 0;
+ return alloc_cache.release();
+ }
+
+ void insert(double val)
+ {
+ if (root == nullptr) {
+ root.reset(alloc_node());
+ root->val = val;
+ return;
+ } else {
+ insert(root.get(), val);
+ }
+ }
+
+ void insert(TreeNode *node, double val)
+ {
+ ++node->children;
+ if (val <= node->val) {
+ // Goes into left.
+ if (node->left == nullptr) {
+ node->left.reset(alloc_node());
+ node->left->val = val;
+ } else {
+ insert(node->left.get(), val);
+ }
+ } else {
+ // Goes into right.
+ if (node->right == nullptr) {
+ node->right.reset(alloc_node());
+ node->right->val = val;
+ } else {
+ insert(node->right.get(), val);
+ }
+ }
+ }
+
+ void remove(double val)
+ {
+ assert(root != nullptr);
+ if (root->children == 0) {
+ assert(root->val == val);
+ alloc_cache = move(root);
+ } else {
+ remove(root.get(), val);
+ }
+ }
+
+ void remove(TreeNode *node, double val)
+ {
+ //printf("Down into %p looking for %f [left=%p right=%p]\n", node, val, node->left.get(), node->right.get());
+ if (node->val == val) {
+ remove(node);
+ } else if (val < node->val) {
+ assert(node->left != nullptr);
+ --node->children;
+ if (node->left->children == 0) {
+ assert(node->left->val == val);
+ alloc_cache = move(node->left);
+ } else {
+ remove(node->left.get(), val);
+ }
+ } else {
+ assert(node->right != nullptr);
+ --node->children;
+ if (node->right->children == 0) {
+ assert(node->right->val == val);
+ alloc_cache = move(node->right);
+ } else {
+ remove(node->right.get(), val);
+ }
+ }
+ }
+
+ // Declares a node to be empty, so it should pull up the value of one of its children.
+ // The node must be an interior node (ie., have at least one child).
+ void remove(TreeNode *node)
+ {
+ //printf("Decided that %p must be removed\n", node);
+ assert(node->children > 0);
+ --node->children;
+
+ bool remove_left;
+ if (node->right == nullptr) {
+ remove_left = true;
+ } else if (node->left == nullptr) {
+ remove_left = false;
+ } else {
+ remove_left = (node->left->children >= node->right->children);
+ }
+ if (remove_left) {
+ if (node->left->children == 0) {
+ node->val = node->left->val;
+ alloc_cache = move(node->left);
+ } else {
+ // Move maximum value up to this node.
+ node->val = elem_at(node->left.get(), node->left->children);
+ remove(node->left.get(), node->val);
+ }
+ } else {
+ if (node->right->children == 0) {
+ node->val = node->right->val;
+ alloc_cache = move(node->right);
+ } else {
+ // Move minimum value up to this node.
+ node->val = elem_at(node->right.get(), 0);
+ remove(node->right.get(), node->val);
+ }
+ }
+ }
+
+ double elem_at(size_t elem_idx)
+ {
+ return elem_at(root.get(), elem_idx);
+ }
+
+ double elem_at(TreeNode *node, size_t elem_idx)
+ {
+ //printf("Looking for %lu in node %p [%lu children]\n", elem_idx, node, node->children);
+ assert(node != nullptr);
+ assert(elem_idx <= node->children);
+ if (node->left != nullptr) {
+ if (elem_idx <= node->left->children) {
+ return elem_at(node->left.get(), elem_idx);
+ } else {
+ elem_idx -= node->left->children + 1;
+ }
+ }
+ if (elem_idx == 0) {
+ return node->val;
+ }
+ return elem_at(node->right.get(), elem_idx - 1);
+ }
+
+ void print_tree(TreeNode *node, size_t indent, double min, double max)
+ {
+ if (node == nullptr) return;
+ if (!(node->val >= min && node->val <= max)) {
+ //printf("node %p is outside range [%f,%f]\n", node, min, max);
+ assert(false);
+ }
+ for (size_t i = 0; i < indent * 2; ++i) putchar(' ');
+ printf("%f [%p, %lu children]\n", node->val, node, node->children);
+ print_tree(node->left.get(), indent + 1, min, node->val);
+ print_tree(node->right.get(), indent + 1, node->val, max);
+ }
+
+public:
+ HistoryJitter(size_t history_length, double multiplier, double percentile)
+ : history_length(history_length), multiplier(multiplier), percentile(percentile) {}
+
+ void update(double timestamp, double frame_duration, size_t dropped_frames)
+ {
+ //if (++num_updates % 1000 == 0) {
+ // printf("%d... [%lu in tree %p]\n", num_updates, root->children + 1, root.get());
+ //}
+
+ if (expected_timestamp >= 0.0) {
+ expected_timestamp += dropped_frames * frame_duration;
+ double jitter_seconds = fabs(expected_timestamp - timestamp);
+
+ history.push_back(jitter_seconds);
+ insert(jitter_seconds);
+ //printf("\nTree %p after insert of %f:\n", root.get(), jitter_seconds);
+ //print_tree(root.get(), 0, -HUGE_VAL, HUGE_VAL);
+ while (history.size() > history_length) {
+ // printf("removing %f, because %p has %lu elements and history has %lu elements\n", history.front(), root.get(), root->children + 1, history.size());
+ remove(history.front());
+ history.pop_front();
+ }
+
+ size_t elem_idx = lrint(percentile * (history.size() - 1));
+// printf("Searching for element %lu in %p, which has %lu elements (history has %lu elements)\n", elem_idx, root.get(), root->children + 1, history.size());
+// fflush(stdout);
+//
+ // Cap at 100 ms.
+ max_jitter_seconds = min(elem_at(elem_idx), 0.1);
+ }
+ expected_timestamp = timestamp + frame_duration;
+ }
+
+ double get_expected() const
+ {
+ return expected_timestamp;
+ }
+
+ double get_jitter() const
+ {
+ return max_jitter_seconds * multiplier;
+ }
+};
+
+void test_jitter_history(const vector<Event> &events, size_t history_length, double multiplier, double percentile, double margin)
+{
+ Queue q;
+ HistoryJitter input_jitter(history_length, multiplier, percentile);
+ HistoryJitter output_jitter(history_length, multiplier, percentile);
+
+ for (const Event &event : events) {
+ if (event.direction == Event::IN) {
+ input_jitter.update(event.t, 0.020, 0);
+ q.add_frame(event.t);
+ } else {
+ double now = event.t;
+ output_jitter.update(event.t, 0.020, 0);
+ q.get_frame(event.t);
+
+ double seconds_until_next_frame = max(input_jitter.get_expected() - now + input_jitter.get_jitter(), 0.0);
+ double master_frame_length_seconds = 0.020;
+
+ seconds_until_next_frame += margin; // Hack.
+
+ size_t safe_queue_length = max<int>(floor((seconds_until_next_frame + output_jitter.get_jitter()) / master_frame_length_seconds), 0);
+ while (q.queue_len() > safe_queue_length) {
+ q.drop_frame();
+ }
+ }
+ if (q.should_abort()) return;
+ }
+ char name[256];
+ snprintf(name, sizeof(name), "history[len=%lu,mul=%.1f,pct=%.4f,margin=%.1f]", history_length, multiplier, percentile, 1e3 * margin);
+ q.eval(name);
+}
+
+int main(int argc, char **argv)
+{
+ static const option long_options[] = {
+ { "max-drops", required_argument, 0, 'd' },
+ { "max-underruns", required_argument, 0, 'u' },
+ { "max-latency-ms", required_argument, 0, 'l' },
+ { 0, 0, 0, 0 }
+ };
+ for ( ;; ) {
+ int option_index = 0;
+ int c = getopt_long(argc, argv, "d:u:l:", long_options, &option_index);
+
+ if (c == -1) {
+ break;
+ }
+ switch (c) {
+ case 'd':
+ max_drops = atof(optarg);
+ break;
+ case 'u':
+ max_underruns = atof(optarg);
+ break;
+ case 'l':
+ max_latency_ms = atof(optarg);
+ break;
+ default:
+ fprintf(stderr, "Usage: simul [--max-drops NUM] [--max-underruns NUM] [--max-latency-ms TIME]\n");
+ exit(1);
+ }
+ }
+
+ vector<Event> events;
+
+ const char *filename = (optind < argc) ? argv[optind] : "nageru-latency-log.txt";
+ FILE *fp = fopen(filename, "r");
+ if (fp == nullptr) {
+ perror(filename);
+ exit(1);
+ }
+ while (!feof(fp)) {
+ char dir[256];
+ double t;
+
+ if (fscanf(fp, "%s %lf", dir, &t) != 2) {
+ break;
+ }
+ if (dir[0] == 'I') {
+ events.push_back(Event{Event::IN, t});
+ } else if (dir[0] == 'O') {
+ events.push_back(Event{Event::OUT, t});
+ } else {
+ fprintf(stderr, "ERROR: Unreadable line\n");
+ exit(1);
+ }
+ }
+ fclose(fp);
+
+ sort(events.begin(), events.end(), [](const Event &a, const Event &b) { return a.t < b.t; });
+
+ test_nodrop(events);
+ test_limit_to_1(events);
+ test_limit_to_2(events);
+ test_nageru_1_2_0(events);
+ for (double multiplier : { 0.0, 0.5, 1.0, 2.0, 3.0, 5.0 }) {
+ for (double alpha : { 0.5, 0.9, 0.99, 0.995, 0.999, 0.9999 }) {
+ for (double margin_ms : { -1.0, 0.0, 1.0, 2.0, 5.0, 10.0, 20.0 }) {
+ test_jitter_filter(events, multiplier, alpha, 1e-3 * margin_ms);
+ }
+ }
+ }
+ for (size_t history_samples : { 10, 100, 500, 1000, 5000, 10000, 25000 }) {
+ for (double multiplier : { 0.5, 1.0, 2.0, 3.0, 5.0, 10.0 }) {
+ for (double percentile : { 0.5, 0.75, 0.9, 0.99, 0.995, 0.999, 1.0 }) {
+ if (lrint(percentile * (history_samples - 1)) == int(history_samples - 1) && percentile != 1.0) {
+ // Redundant.
+ continue;
+ }
+
+ //for (double margin_ms : { -1.0, 0.0, 1.0, 2.0, 5.0, 10.0, 20.0 }) {
+ for (double margin_ms : { 0.0 }) {
+ test_jitter_history(events, history_samples, multiplier, percentile, 1e-3 * margin_ms);
+ }
+ }
+ }
+ }
+}
projects / nageru / blobdiff