[0.15.6] Huge frame drops for no apparent reason

[Ubertwink]

We are playing on Arumba's railworld server. The factory is quite big already, so the game has to be slowed down and we are running at 30 UPS/FPS right now. However, occasionally, intense lag-o-drome storms us, reducing players' FPS down to 2.6-2.7 (while keeping the UPS at 30). During this time, we are unable to move on interact with anything, can't open/close GUI, etc. The time usage debug looks like this:

I'd like to help debugging this problem, as this is certainly not a GPU bottleneck.

[Rseding91]

FPS dropping to 5 while UPS stays up indicates the game is in "catch up" mode - indicating you can't keep up with the server.

[Ubertwink]

How can I track down the reason? The CPU core that's used by Factorio is far from full load and the network is 100Mb/s. Map download speed is about 5-6 MB/s.

[Rseding91]

How can I track down the reason? The CPU core that's used by Factorio is far from full load and the network is 100Mb/s. Map download speed is about 5-6 MB/s.

CPU usage doesn't mean much unless you only have 1 core in your computer. Factorio runs the main logic on 1 thread so the single threaded speed of your CPU is what determines if it can keep up with the server.

There's nothing to "track down" - simply your computer can't keep up with the server because it's not fast enough.

[Ubertwink]

That's right, I see that one of the cores is more loaded than the others. But still, it's far from being fully loaded.
Core clock is above 4 GHz.

[Ubertwink]

There's nothing to "track down" - simply your computer can't keep up with the server because it's not fast enough.

That's it - can you guys please help me to find the weak spot since there is no obvious bottleneck in the system?

[quyxkh]

OP, If a single thread was running 100% of the time but the OS skittered it around among all the different cores every few milliseconds, what would that look like on your GUI monitor?