5 ms·

Wellllll... Ryzen is only 6% behind for multi-core PPW, but The M1 appears to still have a huge advantage in single-core PPW. I have a half dozen thoughts on

Wellllll... Ryzen is only 6% behind for multi-core PPW, but The M1 appears to still have a huge advantage in single-core PPW. I have a half dozen thoughts on this, but the foremost is; Apple keeping memory on chip, is likely providing a huge memory latency advantage, (1) as well as some power benefits. It would not surprise me if this is a large part of (if not the majority) of the advantage here outside of the bigger decoder. Think about a single threaded vs multithreaded benchmark; In the case of ST, there's only one thread the prefetcher can deal with, that one thread is going to be waiting for data. In the case of MT, there's a much greater likelyhood that you'll have multiple threads making memory requests, and the latency can be amortized by having the threads do other work (i.e. Thread 1 can start working on data it got back while thread 2's request is already in-flight from controller to DRAM.) This is one of those moments I miss David Kanter (RealWorldTech, [0]) doing CPU arch breakdowns. (1) - Back in the day, one of the 'better' things you could do for a SDRAM P3/Athlon/Duron system, especially if you were replacing all modules for an upgrade anyway, was to hunt for CL2 memory. [0] - https://www.realworldtech.com/cpu/ https://www.realworldtech.com/cpu/

zekica 4y ago
Exactly - they have on package RAM with 100GB/s and low latency
kcb 4y ago
> Apple keeping memory on chip, is likely providing a huge memory latency advantage How? It's the same LPDDR5 everyone else is using and it's on package not on "chip". The trace length has a negligible impact on latency.
- 0x457 4y ago
  > The trace length has a negligible impact on latency. Uhm, that is not true. If that was true, then your typical motherboard kept slots where they were 10 years ago, but they're getting closer to combat the increase in latency in other places. This is why HEDT motherboards have such layouts. But just getting it close is not enough: M1 has higher memory latency than AMD and Intel SKUs.
pclmulqdq 4y ago
Single threaded perf per watt has never been a benchmark anyone cares about. Perf per watt for the whole die is what counts in power-constrained scenarios. One core on even a 4-core Intel chip (the most power hungry beasts around) cannot hit die-level power or thermal limits.

zekica 4y ago

Exactly - they have on package RAM with 100GB/s and low latency

kcb 4y ago

> Apple keeping memory on chip, is likely providing a huge memory latency advantage How? It's the same LPDDR5 everyone else is using and it's on package not on "chip". The trace length has a negligible impact on latency.

0x457 4y ago
> The trace length has a negligible impact on latency. Uhm, that is not true. If that was true, then your typical motherboard kept slots where they were 10 years ago, but they're getting closer to combat the increase in latency in other places. This is why HEDT motherboards have such layouts. But just getting it close is not enough: M1 has higher memory latency than AMD and Intel SKUs.

pclmulqdq 4y ago

Single threaded perf per watt has never been a benchmark anyone cares about. Perf per watt for the whole die is what counts in power-constrained scenarios. One core on even a 4-core Intel chip (the most power hungry beasts around) cannot hit die-level power or thermal limits.