Update: Apple has officially acknowledged and apologised for the thermal throttling issues on the 2018 MacBook Pro devices. Their response is as follows:
Following extensive performance testing under numerous workloads, we’ve identified that there is a missing digital key in the firmware that impacts the thermal management system and could drive clock speeds down under heavy thermal loads on the new MacBook Pro. A bug fix is included in today’s macOS High Sierra 10.13.6 Supplemental Update and is recommended. We apologize to any customer who has experienced less than optimal performance on their new systems. Customers can expect the new 15-inch MacBook Pro to be up to 70 percent faster, and the 13-inch MacBook Pro with Touch Bar to be up to 2X faster, as shown in the performance results on our website.
We are currently testing the fix on our 2018 MacBook Pro 13 and can immediately report more stable clock speeds and up to 10 percent improvement in performance in certain benchmarks. Expect more details in our upcoming review.
The original story is as follows:
A raft of reports these last few days have indicated that Apple’s fastest, most powerful MacBook Pro ever is suffering from severe thermal throttling issues that are preventing it from reaching its full potential.
The trigger for these reports was a video by YouTuber Dave Lee, who, in the course of reviewing the top end variant of the 2018 MacBook Pro 15, discovered that it was performing slightly worse than the 2017 model it replaced.
This is in itself startling news. The new Intel CPUs are not only faster on paper, they also pack in 50 percent more cores, making them, again on paper, 40-50 percent more powerful than the previous generation model. Add to this the fact that you can spend upwards of $3,000 on the device, and you can see why people are getting worked up.
While Lee isn’t wrong in his assessment, he may not have been entirely correct. Yes, if your work is CPU bound, work that involves heavy video rendering, simulations, machine learning and the like, it’s possible that the Intel Core-i9 powered MacBook Pro is not for you.
For most users, however, this is not a realistic scenario. Various tests by other YouTubers and on various forums and websites have found that the device is, in fact, up to 20 percent faster than previous models in most workloads.
Better yet, it bears mention that every Ultrabook in the market suffers from thermal throttling.
For example, in our testing of the Lenovo Yoga 920 (2018) and Dell XPS 13 (2018), we discovered that under sustained load (50 minutes), the Yoga 920 was 7 percent faster. Under burst loads (20-30 seconds), the XPS 13 was 36 percent faster. Both devices use the exact same CPU— the Intel Core-i7 8550U — but clearly, very different cooling platforms.
In real-world usage, the XPS 13 will perform better. For heavy usage, the Yoga 920 has the edge.
What is thermal throttling?
Whenever a chip (the CPU in this case) does work, it gets hot. More work = more heat. A car engine is the same: the faster it runs, the hotter it gets. Only with adequate cooling can you run a car at a higher speed for longer.
If the cooling system of a car fails, the engine will overheat and get damaged.
For computers, chips are rated for something called TDP or Thermal Design Power. This is the maximum heat output of a chip that a reference cooling system is designed to dissipate. You can use a beefier cooling system and dissipate more heat and you could use a weaker cooling system and dissipate less heat.
Depending on the heat that’s dissipated, the chip will perform better or worse.
In slim Ultrabooks like the MacBook or Yoga 920 or Dell XPS 13, the engineers cannot afford to include beefy cooling solutions. In fact, they can barely include a reference cooling solution. Why? Heat dissipation is all about volume (think litres, not decibels), and space is at a premium in any Ultrabook.
Normally, when a CPU starts getting hot, the laptop will ramp up the speed of the cooling fans to improve air flow. If it gets hotter still, the CPU will be forced to slow down to save itself from damage.
If you put a Ferrari engine in a Maruti 800, that engine will melt. If you slow that engine down to a 1,000 rpm, it might survive in that tiny chassis.
The real issue with the 15-inch MacBook Pro
The 2018 MacBook Pro 15 is being throttled, but as it turns out, thermal issues might not be to blame.
People who are much more knowledgeable than I am noted that the speed of the MBP15 was fluctuating wildly under load. Normally, a thermally-throttled system will run at a slower, but steadier pace. Instead, the MacBook was fluctuating between its lowest clock speed and maximum possible clock speed.
A Reddit user going by username randompersonx thinks he's narrowed down the issue to the MacBook’s VRM configuration. The VRM (Voltage Regulator Module) cleans up and manages the voltage going to the CPU. It’s essential for maintaining the stability of a CPU and is integrated into the motherboard.
According to this user, and some scattered reports, the VRM is inadequate for delivering power to the powerful Core i9 CPU in the MacBook Pro 15 when it’s under load. He claims that the VRM is overheating and that the CPU is being forced to slow down to give the VRM time to cool down. The moment the VRM is sufficiently cool, the CPU is demanding full power because its workload hasn’t reduced in the slightest.
Ideally, the system needs to be configured in such a way that the VRM is sustainably delivering the power that it is designed to deliver. Sure, the overall system will be slower, but the VRM is not under so much stress and the work will finish faster. Fluctuations are grossly inefficient and will cause long-term damage.
Imagine you’re a truck driver and you must deliver something from Mumbai to Pune in the shortest possible time, you could floor it and risk damaging the engine, or you could settle on a cruising speed that won’t kill the engine and make it to your destination in one piece.
Apple’s alleged solution is the equivalent of alternately revving the engine to the max and then idling it and doing this repeatedly until the work gets done.
As the experienced and foul-mouthed, but well-respected and renowned, repair guy Louis Rossman notes, putting the VRM under this much stress means that it could fail within a year or two.
Again, this is a $3,000 device.
What happens if the VRM fails?
Obviously, your MacBook will stop working. Immediately.
Since everything on a MacBook motherboard is soldered on, a failed VRM means you could just buy a new Mac. The repair will necessitate the replacement of basically all the internals of your system, which includes the CPU, RAM and storage.
If the latest rumours are true, it might even be impossible to recover the data from your $3,000 machine.
Why are other MacBooks unaffected?
If indeed the problem is related to the VRM, it’s very likely that the other MacBooks simply don’t draw enough power to strain their VRMs so.
Note: We’ve reached out to Apple for a response. The article will be updated with their response when it arrives.