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diff --git a/docs/logging_and_performance_metrics.md b/docs/logging_and_performance_metrics.md new file mode 100644 index 000000000..9f0679acd --- /dev/null +++ b/docs/logging_and_performance_metrics.md @@ -0,0 +1,101 @@ +# Logging, frame rate and performance metrics + +## 1.0) Logging of potentially dangerous actions + +OpenTTD is a complex program, and together with NewGRF, it may show a buggy +behaviour. But not only bugs in code can cause problems. There are several +ways to affect game state possibly resulting in program crash or multiplayer +desyncs. + +Easier way would be to forbid all these unsafe actions, but that would affect +game usability for many players. We certainly do not want that. +However, we receive bug reports because of this. To reduce time spent with +solving these problems, these potentially unsafe actions are logged in +the savegame (including crash.sav). Log is stored in crash logs, too. + +Information logged: + +- Adding / removing / changing order of NewGRFs +- Changing NewGRF parameters, loading compatible NewGRF +- Changing game mode (scenario editor <-> normal game) +- Loading game saved in a different OpenTTD / TTDPatch / Transport Tycoon Deluxe / + original Transport Tycoon version +- Running a modified OpenTTD build +- Changing settings affecting NewGRF behaviour (non-network-safe settings) +- Triggering NewGRF bugs + +No personal information is stored. + +You can show the game log by typing 'gamelog' in the console or by running +OpenTTD in debug mode. + +## 2.0) Frame rate and performance metrics + +The Help menu in-game has a function to open the Frame rate window. This +window shows various real-time performance statistics, measuring what parts +of the game require the most processing power currently. + +A summary of the statistics can also be retrieved from the console with the +`fps` command. This is especially useful on dedicated servers, where the +administrator might want to determine what's limiting performance in a slow +game. + +The frame rate is given as two figures, the simulation rate and the graphics +frame rate. Usually these are identical, as the screen is rendered exactly +once per simulated tick, but in the future there might be support for graphics +and simulation running at different rates. When the game is paused, the +simulation rate drops to zero. + +In addition to the simulation rate, a game speed factor is also calculated. +This is based on the target simulation speed, which is 30 milliseconds per +game tick. At that speed, the expected frame rate is 33.33 frames/second, and +the game speed factor is how close to that target the actual rate is. When +the game is in fast forward mode, the game speed factor shows how much +speed up is achieved. + +The lower part of the window shows timing statistics for individual parts of +the game. The times shown are short-term and long-term averages of how long +it takes to process one tick of game time, all figures are in milliseconds. + +Clicking a line in the lower part of the window opens a graph window, giving +detailed readings on each tick simulated by the game. + +The following is an explanation of the different statistics: + +- *Game loop* - Total processing time used per simulated "tick" in the game. + This includes all pathfinding, world updates, and economy handling. +- *Cargo handling* - Time spent loading/unloading cargo at stations, and + industries and towns sending/retrieving cargo from stations. +- *Train ticks*, *Road vehicle ticks*, *Ship ticks*, *Aircraft ticks* - + Time spent on pathfinding and other processing for each player vehicle type. +- *World ticks* - Time spent on other world/landscape processing. This + includes towns growing, building animations, updates of farmland and trees, + and station rating updates. +- *GS/AI total*, *Game script*, and *AI players* - Time spent running logic + for game scripts and AI players. The total may show as less than the current + sum of the individual scripts, this is because AI players at lower + difficulty settings do not run every game tick, and hence contribute less + to the average across all ticks. Keep in mind that the "Current" figure is + also an average, just only over short term. +- *Link graph delay* - Time overruns of the cargo distribution link graph + update thread. Usually the link graph is updated in a background thread, + but these updates need to synchronise with the main game loop occasionally, + if the time spent on link graph updates is longer than the time taken to + otherwise simulate the game while it was updating, these delays are counted + in this figure. +- *Graphics rendering* - Total time spent rendering all graphics, including + both GUI and world viewports. This typically spikes when panning the view + around, and when more things are happening on screen at once. +- *World viewport rendering* - Isolated time spent rendering just world + viewports. If this figure is significantly lower than the total graphics + rendering time, most time is spent rendering GUI than rendering world. +- *Video output* - Speed of copying the rendered graphics to the display + adapter. Usually this should be very fast (in the range of 0-3 ms), large + values for this can indicate a graphics driver problem. +- *Sound mixing* - Speed of mixing active audio samples together. Usually + this should be very fast (in the range of 0-3 ms), if it is slow, consider + switching to the NoSound set. + +If the frame rate window is shaded, the title bar will instead show just the +current simulation rate and the game speed factor. + |