Alt-F4 #52 - Fluidic Power Benchmarking  2021-11-12

What is it again?

In last week’s article I talked about the history of Factorio power network overhaul mods and how they worked, and then explained my own take on it called Fluidic Power. It’s recommended that you read that article first, but in a nutshell, I made Factorio’s power distribution more realistic by simulating it as a fluid - using the already built-in fluid simulation mechanics. This means you need to use transformers to minimize voltage drop over distance. It also means that, for example, it is more work to keep your laser turrets firing at 100%, or to build highly beaconed setups.

  An example of biters attacking an outpost with “show-fluid-box-info” turned on. The green bar shows the fluid level and blue shows the fluid speed. Notice the lasers intermittently turning off.

An example of biters attacking an outpost with “show-fluid-box-info” turned on. The green bar shows the fluid level and blue shows the fluid speed. Notice the lasers intermittently turning off.

These new limitations mean that Fluidic Power achieved its goal of creating a new game mechanic that more closely resembles realistic electricity. However, it does introduce significantly more performance overhead with all the new fluid calculations required. I didn’t want to put a mod on the mod portal that will bring your PC to a halt if you built a decently sized factory. So therefore I set out to do some research. Do the extra fluid calculations really have a significant impact?

Is the performance playable?

There is a reason why Factorio implements electricity the way it does. It allows us to build absolutely gigantic factories at such a scale that you can get lost in them. Adding more realistic power might inhibit performance so significantly that you’d have to build smaller factories, and nobody wants to do that. So the question is: What would Factorio’s performance actually be like if there was fluid flowing through each and every power pole. I needed a benchmark map, so I set out to build a pure Fluidic Power base with the help of my friend JanKrater.

My goal for this base was to think of the most performance efficient way to build a base, and to then do the exact opposite (well, mostly). This resulted in a spaghetti base with way too many power poles, very convoluted belts, and way too many power-hungry laser turrets. Very importantly though, it manages to produce a steady 45 science per minute, and it draws about 600 MW with not a single efficiency module in sight.

The benchmark Spaghetti Base running at 45 SPM.

Normally, Factorio runs at about 60 updates per second (referred to as UPS), and I managed to push this benchmark map to run at 70 UPS on my old-ish PC (i7-4770k 3.5GHz CPU, DDR3-1600MHz RAM). This means that it takes about ~14ms to update the whole base once, called one tick, where for 60 UPS the maximum amount of time per update can be 1/60 = ~16.6ms. This number is also shown below in the “show-time-usage” debug output. Interestingly, it also shows that my mod script (mod-FluidicPower) has a neglible effect on the performance (~0.05ms). This is possible because my mod makes very few calculations, as it’s able to offload all the expensive fluid and power calculations to the optimized game engine. The main timing information to look at is Fluid Manager and Electric Network.

In-game “show-time-usage” and “show-entity-time-usage” information of the 45 SPM Spaghetti Base.

In the output above the game tells you where most of the time is spent, and it initially confused me that game seemingly spends most of its time in the Electric Network. My expectation was that the Fluid Manager would take the biggest performance hit, but instead the output shows that the Electric Network (~10ms) is using over 70% of the update time (~13.7ms), and that the Fluid Manager (~0.03ms) doesn’t seem to be doing anything at all. This doesn’t make any sense, because I expected the amount of fluid calculations to be a massive performance drain. I headed to the Technical Factorio community, where they push Factorio’s performance to its absolute limit. Here, the brilliant mathematician SteveTrov explained to me why the in-game time usage can be misleading if you don’t know how the timing calculations are actually implemented. He described it as such:

Firstly, the time usage stats are confusing because the fluid and electric network update are run in parallel threads. This is roughly what happens most of the time:

The electric network thread is started and the electric network update timer is started. The heat update thread is stated Multiple fluid update threads are started. When the electric update thread finishes the time used is recorded under electric network update. The fluid update timer is effectively started now When the fluid threads have all finished (they normally do before step 4) the fluid update timer is stopped.

So the effect of this is that the fluid update time is nearly always very low.

— [SteveTrov](https://discord.com/channels/579345487371567105/579346716243787782/855875612274851881)

This essentially means that the Fluid Manager’s time usage information is entangled in the Electric Network’s and Heat Manager’s time usage. It’s not possible to calculate an accurate metric as to which part takes the most processing time without changing the Factorio game engine itself. I need another approach to know if the Electric Network really is taking more processing time than the Fluid Manager, and if so, by how much?

An UPS expert called flame_Sla then suggested that I download the Very Sleepy Profiler to see detailed information about which of the Factorio engine’s C++ functions are called most often. Their community often use this tool to optimize the world’s largest and most UPS efficient megabases. In the output of the tool below you can see which C++ functions take the most time, listed in descending order. flame_Sla did also mention not to focus on the absolute times shown, but to rather use it as a metric which the biggest culprits can be identified with.

Output of the Very Sleepy profiling tool running on my spaghetti Fluidic Power benchmarking base. On the right is one instance of the call stack of the selected function.

This showed something that I didn’t really expect. The fluid system (FluidSystem::update) was only in the top 10 worst timed functions, and the Electric Network was still taking more processing time! It turns out the main problem was FlowStatistics<ID<...>...>::onFlow, which is mostly called by the electric network. These flow statistics collect the data necessary to view the game’s graphs, eg. the power production window. This means that the game is not only slowing down because of all the new fluid calculations, but also to collect information to draw the graphs for all the new power networks!

It’s very likely that the collection of Electric Network statistics could take a significant amount of processing time with Fluidic Power. The Factorio engine is designed to only have a handful of electric netwo

Should you play it?

Personally, I think Fluidic Power creates a really fun challenge. It’s maybe not for you if you’re planning on building a long-lived megabase, but if you’re looking for an interesting adventure playthrough with new challenges then this mod might just be for you. I really enjoyed overcoming all the new gameplay obstacles it creates. For example, the machines furthest away from your steam engines shut down first, which are usually the electric mining drills on your coal patch that feed your boilers. I hadn’t ever experienced such a dangerous coal death spiral before. Or, if you defend your walls with laser turrets, you’ll need to ensure there are enough transformers to supply power at the correct voltage.

However, my favourite part of this mod by far is knowing that there is actual electricity flowing through the power poles. You can even see the waves of intermittent brownouts over your machines when your base is pulling too much power, like when many laser turrets fire at once. It’s similar to the feeling I get when I look at a circuit I designed, while knowing it’s working because of the fluid-like motion of electrons through the copper and silicon. It builds on the feeling of seeing your complex networks of belts working together to build a rocket. It makes the factory feel more alive. You can basically see its steady heartbeat, and it’s really satisfying.

Contributing

As always, we’re looking for people that want to contribute to Alt-F4, be it by submitting an article or by helping with translation. If you have something interesting in mind that you want to share with the community in a polished way, this is the place to do it. If you’re not too sure about it we’ll gladly help by discussing content ideas and structure questions. If that sounds like something that’s up your alley, join the Discord to get started!

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