+++ /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