Apple M4 MacBook Air – Apple’s Continued Aggressive SoC Power Management
Keeping up my theme of constantly analyzing the battery life of each new Apple M series silicon, I was excited to dive into the new M4 Macbook Air. Every year, gen on gen, Apple continues what their silicon design teams like to call the relentless pursuit of performance per watt. While the M4 is not new, running in the Mac Mini and Macbook Pro SKUs, it is the Air that is Apple’s battery life king and I was interested in how the M4 Macbook Air would compare to prior Macbook Air’s with later generation Apple Silicon. My Macbook Air model is the 15″ 16GB of Memory 6 E-core and 4 P-core CPU and 10 GPU cores.
The Raw Battery Life Benchmarks
I’ll keep this part pretty succinct since it is the most straightforward. We have our proprietary custom battery life script, one that admittedly puts slightly more stress on the device than the basic benchmarks that get used that test video or internet browsing time. Our test browses the web, watches YouTube, creates a document with 500 words of text, and does a 90-second CPU stress test. The total loop is ~15 min and it runs that cycle until the battery is dead. We run all our tests with the display at 150 nits. I like to run multiple tests, one where the system determines the battery mode and one where I leave it on low-power mode.
I like our battery test because it is more of a real-world, day-in-the-life test of how many hours one can expect to actively use the machine, screen on, during a normal day. Our battery benchmark in non-lower power mode (basically balanced mode) got 10 hours of straight usage. In low-power mode the 15″ M4 Macbook Air got 12 hours of continuous usage. Again, this test uses the system to do a wide range of things, meaning I’m confident those are continuous hours of usage doing “light” work. Just browsing the web, or just watching videos the battery lasts much longer. While the battery life is about the same as the M3 Macbook Air, what stood out to us is the addition of two E-cores with M4 which has 6 E-cores and 4 P-cores compared to the M3 Air has 4 E-cores and 4 P-cores. We have stated for multiple generations, really since the M2 Macbook Air, that Apple has continually made the E cores more performant and the P cores more efficient. That stands out in the M4 Macbook Air as we analyzed the system resources during various benchmarks and saw a few very interesting things.
Continued System Optimization In macOS
As I observed with the M2 Macbook Air optimizing software to utilize new CPU designs to get to zero state as often as possible is an efficiency technique. With M2 we observed the P cores being managed to do their task as needed and get to zero state while the E cores carried most of the system load. This has remained the trend, as a whole for the base M series of Apple Silicon as with Pro and Max versions we see more balance and more P-core work. With the M3 Macbook Air Apple’s software optimization started dropping the E cores to zero state as well which demonstrated increased system optimization as having the cores stay in zero state as often as possible keeps the system in its lowest wattage state as long as possible. The obvious benefits here are battery life and total system efficiency.
Apple has built upon the M3 CPU architecture with that enhanced efficiency of the power state of the E-cores but now by adding 2 more E cores to M4, Apple has again added to its lead in performance per watt while the 6 E cores are more than capable to carry the load of the vast majority of tasks on the Macbook Air. Doing a side-by-side analysis of the M3 Macbook Air and M4 Macbook Air taking into account how macOS managed each of them we found the following results.
M4 Macbook Air Battery Benchmark Workload
• E-core frequency dropped to zero 33.48%
• P-core: dropped to zero 86.51%
M3 Macbook Air Battery Benchmark Workload
• E-core frequency: Zero occurrence 23.54%
• P-core frequency: Zero occurrence 81.69%
The evidence here is Apple’s continued advances in system optimization to even better tune the software to silicon meaning the M4 Macbook Air, despite having two more E-cores, and a higher single-core (~20%) and multi-core (~50%) GeekBench score, actually spent more time in a zero frequency state than M3 Macbook Air. And given, that our battery life tests were in the same average range as the M3 Macbook Air, it means you get more performance without sacrificing any battery life in the new M4 Macbook Air.
Four generations of Apple Silicon are in and I think we see the clear trend lines of their silicon design team’s continued efforts to win on performance per watt. This includes slight microarchitecture tweaks, and tightly optimizing macOS to best utilize each new generation of SoC to maximize performance and efficiency. All the kinds of things that only Apple can do.