Hacker News Reader

Comment by jmuguy | Hacker News Reader

That's distressing to hear. For many months I struggled with performance issues and throttling on my Macbook Pro (15 inch, mid 2017). I went down a bunch of rabbit holes, messing with Time Machine backup, paranoia about specific apps pegging the CPU. The issue with one side of the thunderbolt ports running hotter than the other, and maybe that was causing the system to heat up to the point of throttling.

Finally I discovered it was my external monitors - I have have 2 4k monitors connected and I use display scaling on both. This apparently strains the integrated GPU, heats up the system, and caused the throttling. As ridiculous as it was to purchase an external enclosure and video card - that solved the issue. Now the system runs flawlessly.

View on HN

The integrated GPU isn't the problem. The MBP only uses the dGPU for external monitors. The problem is that the dGPU driver/firmware/whatever is broken so it runs at a minimum of 8W even when there's no work to do, overloading the thermals.

The 2019 16" MPB made this problem far worse, raising the minimum dGPU to 18W, making external displays almost completely unusable for more than 1hr at a time unless you put the laptop aside in an external cooling solution (stand and fans) where you can't ergonomically use the integrated keyboard.

That makes me glad I figured things out, and got the eGPU, because I was really close to buying a newer model in hopes that it would fix things.

I really don't understand how this isn't more of an issue for Apple. Surely theres a lot of pros out there using external monitors. Two external monitors is pretty standard - in my previous life as an IT guy we set that up for probably half of our clients.

> Finally I discovered it was my external monitors - I have have 2 4k monitors connected and I use display scaling on both.

M1 (or at least the macbooks) only supports a single external display, problem solved!

This problem still occurs with the latest MBPs even with one 4k monitor. As you mentioned, it's a heat issue. Once I turn on the AC, it starts to pick up speed again.

It's far worse on the new ones (18W vs 8W) and the problem occurs on almost all monitors, even 2560x1440.

How do you know there is performance throttling?

I run a 4K monitor, 1440p gaming monitor, and the internal monitor without issues. Lots of scaling on all of them.

My windows computer has an issue with the 4K monitor. The cursor has notice ticks and other weird refresh issues. I even bought a 2070 and the issues remain.

What GPU enclosure do you use?

I could see "kernel_task" running and eating up CPU, in an attempt to throttle the system and cool things off. At least that's my understanding of it. Basically it came down to process of elimination, although I'm sure someone more experienced in the various fan and temperature readings on the Mac could have diagnosed it sooner.

It completely stopped once I ran the 4k monitors at native resolution, and when I got the eGPU setup.

The enclosure I purchased is the Razer Core X Chroma. One silver lining is it basically acts like a dock - has USB, wired NIC, and powers the system. Video card is a Radeon RX 580.

Reply on news.ycombinator.com