MacBook Pro 2018 thermal throttling explained

Macbook-Pro-2018

Last week Apple unexpectedly updated their whole Macbook Pro line except the entry 13" model without the Touch Bar.

This release like all previous ones were accompanied by a lot of controversies. That Apple might not have fixed the faulty butterfly keyboard regarding which they are facing now three class action lawsuits. The keyboard scandal also resulted in a keyboard service program which brings free defective keyboards replacements in all MacBooks and MacBook Pros produced since 2015. And if you have one of these laptops you'll be covered by this program for the next four years!

People also blamed Apple for only now allowing to opt-in for 32GB of DDR4 ram, previously supposedly unavailable due to higher energy consumption and leaving everyone with one option of having only 16GB of energy efficient LPDDR3 memory when competitors offered 32GB DD4 ram even before 2016.

Besides that Apple is under fire for taking up so long to bring the 8-th gen Intel CPUs, high prices, no chassis changes, #donglelife was brought up, etc.

I personally think this is a good update. Yes, from the outside everything looks the same (except probably the screen is now enabled with True Tone) but on the inside is the real deal. Or at least it should have been.

The new MacBook Pros are carrying even faster than their already pretty fast nVME SSDs with read and write speeds now up to 3GB/s which is the fastest on the market. I wish their Radeon 555X and 560X GPUs where that advanced, when the portable PC market has Nvidia's GTX 1060, 1070 and sometimes even 1080s onboard. The same is for screen resolution - Apple ships the same 2880x1800px since 2012 when at that time it definitely was a blast and on which it's still hard to recognize individual pixels on a 15" diagonal. But in the meantime the competing devices in the high-end market like the Surface Book 2 from Microsoft caught up with screens as dense as 3000x2000px on a 13" area!

So besides the fastest storage and irreplaceable MacOS limited to Apple's hardware the only real advantage of MacBook Pros was the CPU.

I'm the owner of a 2016 top of the line Macbook Pro 15". Maybe I'm lucky or because I use it in clamshell mode most of the time, I got only one stuck key in the 16 months of owning this device. But oh I couldn't escape the issues with dongles and expensive USB-C cables which in real life is far from mass adoption and except being able to charge my laptop from both sides was mostly a pain to use.

But the main reason I chose the laptop at that time was to have a more powerful machine then my previous 2015 MacBook Pro 13" which wasn't a slouch either but when it comes to compiling (which I do most of the time) the more horsepower you have - the better. And moving from 2 cores of the 13" to 4 cores in the 15" resulted in 3-4x faster compiling times.

At that time I was more than satisfied with my 15", using it daily at home and on the go. Among all possible options it was the most CPU power you could have in a small light chassis, period. I'm still not considering a desktop because I don't want to manage project files sync between a desktop and mobile computer so I wanted as much performance in as little footprint I can have - and the MacBook Pro is the best candidate for that role. Especially when you don't consider much Windows as your primary work OS 🙂

During my use of the laptop I ignored few messages on Twitter about thermal throttling in the 2016-2017 MacBook Pros. For example when you connect it to a HiDPI screen, the integrated Intel GPU switches to the discrete Radeon GPU and that automatically increases the baseline heat the laptop has to deal with. And you can beat heat in two ways: increasing fan speed and cooling the system more, or decreasing CPU clock speed, make it less efficient in heat production but also in it's own performance.

In the last few years that's where CPU design generally was heading. In order to achieve longer battery life and potential high performance, Intel, the main CPU supplier was making CPUs more efficient when idle to preserve battery on light tasks and to give performance bursts on more demanding ones. That's why CPU clock speeds are no more static like they were before. Now instead of '3.1 Ghz' clock speed, you would see '2.6-4.3 Ghz' on the box, which means 2.6 Ghz as base clock with bursts up to 4.3Ghz. And when a CPU generates heat, it can't sustain being in the high (called 'Boost') levels for long and has to lower the clock speed not to overheat. That's what Thermal Throttling means

My laptop was also thermal throttling, I just didn't know how much. I knew it did, but I wasn't giving it much attention. But this week I did.

The thing is the new MacBook Pros introduced new 6 core CPUs in the 15" line and bumped the core count from 2 to 4 in 13" and I was really excited about the increased core counts recalling how much performance I gained last time after switching from 2 to 4 cores. I was thinking whether to switch to a smaller lighter 13" from my 15" and keep my current 4 cores or upgrade to 6 cores and achieve ultimate mobile power. Usually preferring more power I was leaning more towards the latter. And by latter I mean I was looking again into the top of the line option of the 15" MacBook Pro with an Core i9 CPU.

And this is when thermal throttling concerns came back:

Under short load, to finish benchmarks, the i9 CPU shows excellent results. In the mobile CPU chart the specific Intel Core i9-8950HK as of now holds #7 in overall mobile CPU rating in terms of performance which is huge. In coincidence the i9 MacBook Pro scores #7 in all-time Geekbench multi-core results loosing only to the 10-18 core beast iMac Pro desktop.

But when it comes to this CPU being under load for a long time, it's results are not so promising. Being hot for a long time, combined with Apple's love to spin down the fans to reduce noice and making the laptops unnecessary thin with sacrifices to cooling, this results in CPU thermal throttling when its clock speed is not only not capable of Boosting up to 4.8Ghz but sometimes drops even lower it's 2.9Ghz baseline! This way the CPU and thus the whole laptop at high loads works only on a fraction of it's potential. And a last year's less powerful CPU with less cores throttling less blows the new 6 core i9 chip out of the water!

What does this mean for a regular customer? That it's not worth paying extra for the high tier model since at peaks it may be slower than the low tier model within the same line. And for a non-regular user that means Apple tries selling you more expensive laptop that performs worse than cheaper models. And all of that on top of the already increased prices introduced along the new USB-C only design in 2016.

One of the reasonable theories of putting a hot CPU in the chassis that wasn't really designed for it that I've heard is that Apple while designing the chassis long before 2016 was relying on Intel's promises to reduce their technology process in timely manner which would help building and using less hot CPUs in 2018 and onwards. And when Intel couldn't keep up with their promises, it was too late for Apple to design new chassis for that. But the main question remains: if Apple knew they won't get more efficient and cooler CPUs, why they even put the severely throttling i9 version in their Stores in the first place? I surely hope it was a mistake rather than trying to earn on top models despite knowing their limitations upfront.

Update Jul 24
Apple released a software fix for throttling in the whole 2018 Macbook Pro line. They claim they fixed an issue with power management and didn't address the supposedly VRM throttling problem that was revealed in one of the Reddit threads. In any case that is good news, the CPU frequency spikes aren't there anymore according to users with the i9 MacBook Pro. Unfortunately the fix won't change the state of the case not being able to handle higher thermals and limiting the i9 from boosting. But at least the frequency now shouldn't fall below it's baseline which is better than nothing 🙂