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Interesting, I didn't know that the memory latency was worse. The bandwidth is still much higher right? In your estimation how much of the perf gains of the M1

Interesting, I didn't know that the memory latency was worse. The bandwidth is still much higher right? In your estimation how much of the perf gains of the M1 chip are due to the increased memory bandwidth vs other optimizations/advancements?

formerly_proven 5y ago
I don't think you can single out one aspect when comparing designs which are so different, but I'd say most of the CPU performance is down to the core. There you have the M1 core which is (iirc) 10 pipes wide, much wider than both AMD and Intel, and a much fatter frontend as well to feed the beast. I think that's the main advantage the M1 has. It also has a larger L1 cache (twice as big as x86). These two are one of the few areas where x86 has an innate disadvantage because fattening up the frontend is much more complex on x86 compared to ARM, and you can't have a VIPT L1 cache larger than 64K with 4K pages, which is a hard-to-change default on x86, while the M1 by default uses larger pages (32K or something like that).
- errantspark 5y ago
  "x86 has an innate disadvantage [...] fattening up the frontend" this is inherent largely because of ISA complexity and variable width instructions? "M1 core which is [...] much wider than both AMD and Intel" The core width you're referring to is the decoder width yeah? As another poster pointed out the M1 has a large reorder buffer as well. Combined with the ability to index a larger L1 cache what I'm getting here is that the M1 can be a lot better about scheduling instructions (and perhaps even running non-interfering instructions in parallel on a given core (is that a thing?)) because the frontend has more power and space to do so. I guess that efficiency is then a big part of the puzzle on why the increased bandwidth to ram makes such an impact?
sliken 5y ago
Many things don't push the memory bandwidth and are cache friendly. However GPUs are bandwidth limited and the M1 Max does quite well against any other integrated graphics from Intel or AMD. Even on the CPU side it can be a big win, in particular on SpecFPRate (a collection of heavy floating point real world codes, not microbenchmarks) Anand has this to say: The fp2017 suite has more workloads that are more memory-bound, and it’s here where the M1 Max is absolutely absurd. The workloads that put the most memory pressure and stress the DRAM the most, such as 503.bwaves, 519.lbm, 549.fotonik3d and 554.roms, have all multiple factors of performance advantages compared to the best Intel and AMD have to offer. To drive this home compare the Spec2017 FP Rate, the M1 Max gets 81.07, the Ryzen 5950x (high end desktop with twice as many fast cores and a 105 watt TDP) gets 62.27. So a low power M1 Max with half as many cores and much lower power is 30% faster than AMD's highest end desktop chip. Instead of a desktop size/volume/power, you can get it in a laptop that's 2/3rd of an inch thick.

formerly_proven 5y ago

I don't think you can single out one aspect when comparing designs which are so different, but I'd say most of the CPU performance is down to the core. There you have the M1 core which is (iirc) 10 pipes wide, much wider than both AMD and Intel, and a much fatter frontend as well to feed the beast. I think that's the main advantage the M1 has. It also has a larger L1 cache (twice as big as x86). These two are one of the few areas where x86 has an innate disadvantage because fattening up the frontend is much more complex on x86 compared to ARM, and you can't have a VIPT L1 cache larger than 64K with 4K pages, which is a hard-to-change default on x86, while the M1 by default uses larger pages (32K or something like that).

errantspark 5y ago
"x86 has an innate disadvantage [...] fattening up the frontend" this is inherent largely because of ISA complexity and variable width instructions? "M1 core which is [...] much wider than both AMD and Intel" The core width you're referring to is the decoder width yeah? As another poster pointed out the M1 has a large reorder buffer as well. Combined with the ability to index a larger L1 cache what I'm getting here is that the M1 can be a lot better about scheduling instructions (and perhaps even running non-interfering instructions in parallel on a given core (is that a thing?)) because the frontend has more power and space to do so. I guess that efficiency is then a big part of the puzzle on why the increased bandwidth to ram makes such an impact?

sliken 5y ago

Many things don't push the memory bandwidth and are cache friendly. However GPUs are bandwidth limited and the M1 Max does quite well against any other integrated graphics from Intel or AMD. Even on the CPU side it can be a big win, in particular on SpecFPRate (a collection of heavy floating point real world codes, not microbenchmarks) Anand has this to say: The fp2017 suite has more workloads that are more memory-bound, and it’s here where the M1 Max is absolutely absurd. The workloads that put the most memory pressure and stress the DRAM the most, such as 503.bwaves, 519.lbm, 549.fotonik3d and 554.roms, have all multiple factors of performance advantages compared to the best Intel and AMD have to offer. To drive this home compare the Spec2017 FP Rate, the M1 Max gets 81.07, the Ryzen 5950x (high end desktop with twice as many fast cores and a 105 watt TDP) gets 62.27. So a low power M1 Max with half as many cores and much lower power is 30% faster than AMD's highest end desktop chip. Instead of a desktop size/volume/power, you can get it in a laptop that's 2/3rd of an inch thick.