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Comment by ShamelessC | Hacker News Reader

I've admittedly never actually considered the dis/advantages of running two CPU's on one board.

Is it correct that you can run two different processors with these? How much of a speedup does it give you? Is the operating system designed to take full advantage of both by default?

Why don't gaming builds use these? Too much cost?

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The same processors should be used, I would be surprised if different one would work together. The processor model has to support two socket operation, those are more expensive. Speedup happens only if the running system benefits from more cores. The expected speedup is <2. Operating systems work with this, but Windows may have some weird problems with many core processors.

Gaming builds usually cannot take advantage of so many cores. Even if the machine is running the game and streaming, single 6-core or 8-core processor is enough.

> The same processors should be used

This is an interesting thing. I should be possible to be smarter about different timings. ARM has very mature asymmetric core support for quite some time now. Intel will soon launch their own in the mobile space.

> Gaming builds usually cannot take advantage of so many cores

Indeed. Games have long been limited in their support for multiple cores. It's a bit surprising because consumer Windows, while it took its time to be able to support multiple sockets, has been able to support them for a very long time now.

It's mostly that the kind of CPU work games are doing is quite hard to parallelise (physics simulations, NPC 'AI', loading and decompressing model data). It's a lot of fairly complex code and getting a synchronisation strategy which actually produces speedup is hard. And when it is done it's usually still limited to e.g. 1 thread doing physics, 1-2 threads doing rendering (it took a while for graphics APIs to support any kind of multi-threaded rendering), etc so it only scales to 3-4 cores max (and there are games which do this, so core count is not completely irrelevant).

Could it explain why we are seeing more improvements in rendering quality compared to physics and AI?

As you said, AI and physics are inherently not really parallelizable while rendering is. AI and physics from the Athlon 64/Pentium 4 era (e.g. Half-Life 2, Crysis) are similar to what we get now, while visual quality greatly improved (better textures, more detailed objects, longer visibility range).

I think for AI the core reason is more sophisticated AI isn't particularly great from a game design POV. In a game, predictability is key, both because a) it allows the game designers to actually change the AI behaviour to balance it and be able to incorporate it into their game design, and b) if the players can't predict the AI they can't plan around it, and the ability to make a plan around a game's systems and try to execute it is a key part of non-frustrating gameplay in most games. The more state-of-the-art AI systems tend to become less predictable and for the most part that makes the games less fun.

In terms of physics usually the issue is if you have a rich physics envrionment it gets more fragile: it's easier for players to break it, intentionally or unintentionally. I've played some games with physics systems far in advance in terms of number of objects than could be achieved previously and they are all pretty much just 'buggy', not necessarily in terms of coding quality, just in terms of how rigid body physics is really prone to creating edge cases which create massive forces, velocities, and/or accelerations from apparently benign arrangements of objects.

I think you're right; at least it jives with everything I've read about game dev. a common design goal in modern games is to never allow the game to fall into a state where forward progress is impossible due to a player action (excepting stuff like dying, of course). realistic physics simulation adds a lot of weird edge cases that need to be tested or hacked around. unlike cs:go, cs:source had lots of collidable physics props in the maps. they looked benign at first, but malicious players could use them to block important passages, make it impossible to defuse the bomb, or arrange them in ways that other players would get stuck in them.

here's a video of hl2 devs reacting to a speedrun of the game using many exploits: https://www.youtube.com/watch?v=sK_PdwL5Y8g

kind of a long video, but there's a lot of interesting commentary on how much work it was to make the physics puzzles robust against unexpected player actions.

I have no experience with game development, but I have some experience in HPC physics simulations. Many physics simulations are embarrassingly parallelizable. I suspect that this is mostly a latency/throughput kind of balance for real time simulations. In games the results have to be ready the next frame.

Alder Lake from Intel will have a big and little core layout.

It'll be fascinating to see how OSs deal with it.

We always use dual (Xeon) systems here--because we need as many PCI lanes as we can get for 4 GPU systems. Getting enough PCI lanes is one main reason people run dual CPU systems.

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