Comment by adrian_b

Comment by adrian_b 7 days ago

1 reply

Single core yes, but multi core no.

The Geekbench scores cannot compare laptop CPUs with desktop CPUs, because the tasks that are executed are too short and they do not demonstrate the steady-state throughput of the CPUs. The desktop CPUs are much faster for multithreaded tasks in comparison with laptop/tablet CPUs than it appears in the GB results.

The Apple CPUs have a much better instructions-per-clock-cycle ratio than any other CPUs, and now in M4 they also have a relatively high clock frequency, of at least 4.5 GHz. This allows them to win most single-threaded benchmarks.

However the performance in multi-threaded benchmarks has a very weak dependence on the CPU microarchitecture and it is determined mostly by the manufacturing process used for the CPU.

If we were able to compare Intel, AMD and Apple CPUs with the same number of cores and made with the same TSMC process, their multithreaded performance would be very close at a given power consumption.

The reason is that executing a given benchmark requires a number of logic transitions that is about the same for different microarchitectures, unless some of the design teams have been incompetent. An Apple CPU does more logic transitions per clock cycle, so in single thread it finishes the task faster.

However in multithreaded execution, where the power consumption of the CPU reaches the power limit, the number of logic transitions per second in the same manufacturing process is determined by the power consumption. Therefore the benchmark will be completed in approximately the same number of seconds when the power limits are the same, regardless of the differences in the single-threaded performance.

At equal power, an M4 will have a slightly better MT performance than an Intel or AMD CPU, due to the better manufacturing process, but the difference is too small to make it competitive with a desktop CPU.

wtallis 7 days ago

> The Geekbench scores cannot compare laptop CPUs with desktop CPUs, because the tasks that are executed are too short and they do not demonstrate the steady-state throughput of the CPUs. The desktop CPUs are much faster for multithreaded tasks in comparison with laptop/tablet CPUs than it appears in the GB results.

Bullshit. What you're talking about is the steady-state of the heatsink, not the steady state of the chip. Intel learned the hard way that a fast CPU core in a phone really does become a fast CPU core in a laptop or desktop when given a better cooling solution.

> However in multithreaded execution, where the power consumption of the CPU reaches the power limit, the number of logic transitions per second in the same manufacturing process is determined by the power consumption. Therefore the benchmark will be completed in approximately the same number of seconds when the power limits are the same, regardless of the differences in the single-threaded performance.

No, microarchitecture really does matter. And so does the macro architecture of AMD's desktop chips that burn a huge amount of power on an inefficient chip to chip interface.