Why does the Xcode simulator launch those fans?

[patent10021]

There are a few videos out in the wild comparing Xcode build times using command-line scripts and measuring temperature etc but nothing about the root cause of the increased temperatures when using the Xcode simulator. Everyone says the 16" by default has better thermals simply because the chassis is larger so that's why it is quieter than the 14" M1, but no one really talks about why the simulator has caused the fans to blow so much all these years (including on M1 MBPs).

What does the simulator desire more? CPU, RAM, or GPU? Why does the Xcode simulator cause the fans to blow more than any other pro Mac app?

I've noticed that the fans start up when we build something which triggers the simulator. So does that mean it's not really the simulator but the building of the project that triggers the fans? If so, that would mean CPU+RAM right? Or does the sim definitely require GPU to simulate a device?

I'd like to base my M1 purchasing decision on these factors.

 

[yitwail]

I only have a 16mb M1 Air, but when iOS Simulator launches, it briefly uses all 8 cores, then it settles down to using the 4 efficiency cores, only. So there's some intensive CPU activity at launch. This was with one simulator instance, displaying a YouTube video, so depending on what you do with simulator, I suppose results could differ. I only use Simulator and don't actually do builds with Xcode, so can't comment on how that effects CPU. Anyway, it's nice that the CPU usage settles down quickly.

 

[patent10021]

But the fans often start spinning even with empty storyboards. Even if it's just code and you run the app which then opens the simulator, the fans launch. Xcode has been like that since the beginning. Does that mean it's a CPU/RAM hog? has nothing to do with GPU?

 

[synicalx1]

You can see what it's doing if you fire up Activity Monitor, and if you want to check what it's doing to your GPU you'll need to turn that on separately in AM.

I'm assuming firing up a virtual iPhone is at least a little intensive across the board. For example if you fire up a regular virtual machine and just leave it running, you'll see your load average sitting higher than normal even if the VM isn't doing anything. I can only assume an iPhone with it's fancy UI and harder-to-emulate hardware is probably a little more demanding than that.

 

[patent10021]

You can see what it's doing if you fire up Activity Monitor, and if you want to check what it's doing to your GPU you'll need to turn that on separately in AM.

I'm assuming firing up a virtual iPhone is at least a little intensive across the board. For example if you fire up a regular virtual machine and just leave it running, you'll see your load average sitting higher than normal even if the VM isn't doing anything. I can only assume an iPhone with it's fancy UI and harder-to-emulate hardware is probably a little more demanding than that.

So do you think an M1 for Xcode would be best served with more RAM, CPU cores or GPU cores?
RAM is usually effective for multitasking and multiple instances etc. You can only get either 8 or 10 CPU cores with the 14" M1 Pro so neither of those would make much difference. So maybe I should bump up the GPU cores to 24? But I heard that the fans on M1 machines will kick in more if the machine has more GPU cores because with more GPU cores the machine gets hotter therefore needs more cooling.

 

[synicalx1]

So do you think an M1 for Xcode would be best served with more RAM, CPU cores or GPU cores?
RAM is usually effective for multitasking and multiple instances etc. You can only get either 8 or 10 CPU cores with the 14" M1 Pro so neither of those would make much difference. So maybe I should bump up the GPU cores to 24? But I heard that the fans on M1 machines will kick in more if the machine has more GPU cores because with more GPU cores the machine gets hotter therefore needs more cooling.

I haven't used Xcode in a few years, but anecdotally I've found it to perform quite well with more CPU and memory regardless of what GPU is on offer.

Maybe 3-4 years back I had a small iOS dev team I looked after and most had 13" MBPs with integrated graphics but as much RAM and the biggest CPU's we could give them and they never had any major issues, however we did delegate most build tasks to a souped up trash can Mac Pro which was (at the time) very high-end.