iPhone 6 takes massive performance hit after Spectre patch

12 January 2018

We always knew that patching the recently-discovered Meltdown and Spectre vulnerabilities will involve a drop in performance, especially in older devices. The magnitude of the drop is still being examined, but the early results don’t look good.

In at least one case, an iPhone 6 saw its Apple A8 lose 40% of its CPU performance after going from iOS 11.1.2 to 11.2.2. The test was run by Dutch entrepreneur Melvin Mughal who got the following results on his phone before and after the update.

	Before Spectre update	After Spectre update	Performance change
iPhone type	iPhone 6
iOS version	iOS 11.1.2	iOS 11.2.2
Single-Core Score	1561	924	-41%
Multi-Core Score	2665	1616	-39%

Both single and multi-core performance are strongly affected and memory access took a hit as well. That was to be expected as both vulnerabilities exploit the CPU’s cache.

Since the test was run on the same phone, the scores are not affected by the battery-related slowdown. That does make it harder to collect more data, however.

For example, here’s one result from Geekbench’s database where the scores remain on pre-update levels and another one, which is closer to Melvin’s numbers. There are more 11.2.2 scores like that, but it’s hard to tell how much of the inconsistency is due to throttling due to an old battery.