Apple MacBook Pro bug patched, unleashing full-speed performance (updated)

The bug affected all new 2018 MacBook Pro laptops, but the MacOS update is already showing promising results.

Dan Ackerman Editorial Director / Computers and Gaming
Dan Ackerman leads CNET's coverage of computers and gaming hardware. A New York native and former radio DJ, he's also a regular TV talking head and the author of "The Tetris Effect" (Hachette/PublicAffairs), a non-fiction gaming and business history book that has earned rave reviews from the New York Times, Fortune, LA Review of Books, and many other publications. "Upends the standard Silicon Valley, Steve Jobs/Mark Zuckerberg technology-creation myth... the story shines." -- The New York Times
Expertise I've been testing and reviewing computer and gaming hardware for over 20 years, covering every console launch since the Dreamcast and every MacBook...ever. Credentials
  • Author of the award-winning, NY Times-reviewed nonfiction book The Tetris Effect; Longtime consumer technology expert for CBS Mornings
Dan Ackerman
4 min read
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Apple has been catching heat over the performance of its new MacBook Pro laptops, but the company is hoping its new software update will help cool off outraged power users. 

After reports of heat issues leading to throttled performance, Apple has determined that a simple software bug was to blame, and has released what it hopes is a quick fix. In our initial testing, the MacOS update appears to correct the up-and-down CPU throttling, and we're continuing to run additional tests.  

Watch this: Apple promises to fix MacBook Pro CPU throttling bug

"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," an Apple spokesperson tells CNET. "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."

Instructions for how to install the MacOS 10.13.6 update are available here. The issue affects all of Apple's new MacBook Pro models, both 13- and 15-inch. The entry level 13-inch MacBook Pro without the Touch Bar isn't affected, as it has not been updated this year.

The surprise midsummer update to the 13- and 15-inch MacBook Pro line, announced July 12, includes new eighth-gen Intel CPUs, up to the high-end, six-core Core i9 in the 15-inch MacBook Pro. Also new are bigger solid-state storage drives, an updated T2 security chip and a True Tone screen that adjusts color temperature based on the available light. But while that makes for a substantially updated product, much of that had been overshadowed by the early performance issues. 

Heat throttling during intense workloads

The biggest initial buzz about the new MacBooks -- aside from an ongoing controversy over how much its keyboard did or didn't change -- came from some early adopters who claimed the premium Core i9 versions, which cost a minimum of $2,799, were prone to heat-related throttling. That means the laptops dropped their CPU clock speed when internal temperatures spiked, leading to slower performance than older models with less-advanced Core i7 processors.

YouTube tech personality Dave Lee first brought the issue to public attention with a video in which he demonstrated the heat and throttling issues. These results were soon replicated by others, including a weekend demo session from Leo Laporte on The New Screen Savers

The problems only became evident when running long, intense processes, such as encoding longer 4K videos. Here in the CNET Labs, where we're testing a $4,699, 15-inch, Core i9 configuration of the new MacBook Pro, the new model showed performance improvements over last year's Core i7 MacBook in our initial tests, which were short enough so as not to trigger the heat-related throttling.

When setting up an intensive workload to deliberately push the system, however, we were able to easily cause the Core i9 CPU in our 2018 MacBook Pro to ping-pong its internal temperature and CPU clock speed up and down rapidly, in both a video encoding and 3D gaming test. (This was before applying Apple's newly announced patch.)

In comparison, the 2017 15-inch MacBook Pro maintained a much more even temperature and CPU clock speed while performing the same tasks.


On the left, a 2017 Core i7 MacBook Pro runs a video encoding test. On the right, a 2018 Core i9 MBP sees its internal temperature and CPU clock speed throttle up and down wildly while performing the same task. 

Dan Ackerman/CNET

So, while not all users would see their performance compromised by the heat throttling issues, the sort of power users who would be rendering long-form, high-res video would. Those are the pro users to whom Apple was targeting this round of updates -- and the exact same people who don't want to pay $6,699 for a top-line configuration, only to find out that it can't perform as well as an older version on the most intense tasks. (Imagine buying a Ferrari, only to be told you can't exceed 60 mph for more than 5 minutes at a time.) And that's why the initial excitement over the surprise MacBook Pro update quickly turned to several days of negative headlines, alarmed Mac enthusiast podcasts and disappointed Mac users sounding off in Reddit threads. 

But the patch, issued by Apple less than two weeks after the new laptops were announced, may well turn the tide.

Promising early results from new software fix

Once Apple released the update, we installed it on our Core i9 15-inch MacBook Pro and repeated some of the same tests. Now, the CPU throttling has stopped, and the clock frequency of the CPU and internal system temperature both remain fairly stable, even when running a 4K video encode or a game set to maximum detail settings.  


The out-of-the-box 2018 MacBook Pro, now on the left, compared to the same laptop (right), running the same test, after installing Apple's new patch. 

Dan Ackerman/CNET

CNET Labs will continue to test the new MacBook Pro with Apple's software patch and will include updated performance results in our full review.

This article was originally published at 1pm ET on July 24, 2018. It has been updated with additional test results after installing the latest Apple MacOS patch. 

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