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We'll get a live test of this very soon - Zen4 is going to be going head-to-head against Apple A16 (Apple's next core architecture) on TSMC N5P next year. Does

by paulmd 5y ago

We'll get a live test of this very soon - Zen4 is going to be going head-to-head against Apple A16 (Apple's next core architecture) on TSMC N5P next year. Does anyone expect x86 to close a factor-of-6 perf/watt difference? (from Anandtech's M1 Max preview) A factor-of-2-to-3 IPC difference? And that's just A15, not against the next-gen A16. Node makes a big difference, it doesn't close up a factor-of-3 IPC gap in a single node though, that's facially ridiculous. Name a full-node shrink+architectural step that has tripled IPC in the last 10 years. Now name one that has done it while cutting power in 1/6th. At that point we will see the goalposts shift again and it will be "well, x86 could do it if they wanted but Apple is just more willing to spend more transistors..." Fact of the matter is the x86 makes it very difficult to spend those transistors efficiently - otherwise it already would have been done. If it was such an obvious gain to just spend those extra transistors, then surely AMD would have done it, if nobody else. Everyone acknowledges x86 has some problems, but the other thing is that they've already mostly played their hand trying to fix those problems, the known solutions like instruction cache have mostly been exhausted at this point. The idea that AMD and Apple can just triple IPC at a whim but they've chosen not to do so for some reason, is facially ridiculous. I know what Jim Keller said but the math just doesn't add up on it for me. OK, full node shrink, great, even if that doubles your transistor count at iso-power, or even doubles it at a little less power, that doesn't double your IPC let alone triple it, and it doesn't close a factor-of-6 perf/watt gap.

TomVDB 5y ago
> Does anyone expect x86 to close a factor-of-6 perf/watt difference? The one number that surprised me in this review was that the perf/W of Threadripper for the rendering phase: it is very close to the M1 Max. I understand that the numbers are not apples to apples because of the total laptop vs CPU-only comparison, but the power consumption of the Threadripper CPU itself is very high and probably takes the lion's share of the overall power consumption. And that's for a previous generation Threadripper.
- paulmd 5y ago
  task energy comparisons are usually won by the processor that gets it done fastest in absolute terms: because of the overhead of the rest of the system, it takes a really big perf/watt win to come out ahead of the system that maybe isn't as efficient in actual watts but gets it done in half the time, because you pay the system overhead for a shorter period of time. it's also a 128-thread processor being put against a 8+2 thread processor, and that's the closest thing to something that will outweigh Apple's IPC advantage here: super wide processor clocked super slow, and unlike the more realistic comparisons (laptop processors, etc) the Epyc has deployed over four times as much silicon just to match the M1. This is the absolute best-case scenario for x86 - they get six times as much silicon and 16 times as many threads and all they can do is match it. Do the comparison again against the Mac Pro 40-core chip when it comes out and you'll see A15 pull ahead again.
  - nathanielarmer 5y ago
    I think you're getting a bit confused. The 3990x is not designed for energy efficiency, on an older node, and on an older architecture... uses 3kWh vs Apples 2kWh (using a very flawed methodology). An yet you're claiming Apple has a 3-6x power efficiency advantage. I'm not sure how that makes any sense.
    - paulmd 5y ago
      Hmm? Perf/watt isn’t the same thing as task energy, it sounds like you’re the one confused here. As I said, task energy (which is what’s measured in the OP) heavily favors “getting it done quicker” as well as this task being embarrassingly parallel such that the 3990WX can get all 128 threads into play. It’s basically a “race to sleep” benchmark not a perf/watt benchmark with processors that are that disparate. For a task energy test - which is not the same thing as a perf/watt test - this is completely loading the dice in favor of x86 and M1 still manages to match it. That is an extremely good result for putting a laptop chip against a top of the line HEDT processor in a test that is normally all about race to sleep. > An yet you're claiming Apple has a 3-6x power efficiency advantage. I’m not the one claiming anything, if you disagree with Anandtech’s numbers go take it up with them. The numbers don’t change just because you find them uncomfortable. > In multi-threaded tests, the 11980HK is clearly allowed to go to much higher power levels than the M1 Max, reaching package power levels of 80W, for 105-110W active wall power, significantly more than what the MacBook Pro here is drawing. The performance levels of the M1 Max are significantly higher than the Intel chip here, due to the much better scalability of the cores. The perf/W differences here are 4-6x in favour of the M1 Max, all whilst posting significantly better performance, meaning the perf/W at ISO-perf would be even higher than this. > In the SPECfp suite, the M1 Max is in its own category of silicon with no comparison in the market. It completely demolishes any laptop contender, showcasing 2.2x performance of the second-best laptop chip. The M1 Max even manages to outperform the 16-core 5950X – a chip whose package power is at 142W, with rest of system even quite above that. It’s an absolutely absurd comparison and a situation we haven’t seen the likes of. https://www.anandtech.com/show/17024/apple-m1-max-performance-review/3 https://www.anandtech.com/show/17024/apple-m1-max-performanc... And again, that’s with it running at half the clock and half the threads of its laptop peers, so IPC is something like 8x higher in those scenarios. That is not the kind of gap you close up with a node shrink or tightening pitches a bit. Hackernews experts know best though. Next year Zen4 and A16 will be on the same node, and then it’ll be another excuse for why x86 is still getting dumpstered. Just keep the goalposts on wheels, you’ll need it.
throwawaylinux 5y ago
I don't really know where to start on this. SKUs that target very different markets are necessarily going to have different performance and efficiency tradeoffs. And core which target different cycle times are going to be able to achieve different IPC. This clearly confuses the basis of performance and different freq/ipc design points. I also didn't suggest Apple would never have the best chips ever. Clearly all else being equal if ISA was irrelevant and you had 1 ARM competitor and 1 x86 competitor then sometimes the ARM CPU is going to be the better of the two. I'm asking is there some continued effect by which people think ARM is going to continue to pull ahead. Is it going to remain < 5%, or is there some turning point where that will start to increase? I'm no expert on this, but there are experts who don't seem to think that there will be such an inflection point.
- paulmd 5y ago
  > I don't really know where to start on this. SKUs that target very different markets are necessarily going to have different performance and efficiency tradeoffs. And core which target different cycle times are going to be able to achieve different IPC. This clearly confuses the basis of performance and different freq/ipc design points. see my response elsewhere, but these aren't unrelated problems: Apple has higher IPC at a lower power-per-core. You can slide around where on the scale x86 falls - maybe you can match perf/watt but then you're getting wiped by a factor of 3 on performance, and you can match on performance but then you're getting wiped by a factor of 6 on perf-watt. You can't do both at once. There simply isn't enough transistor gain from a single node shrink there to clear that much of a gap, basically Apple is also seeing much better performance-per-transistor and that's a harder gap to close. > I'm asking is there some continued effect by which people think ARM is going to continue to pull ahead. Is it going to remain < 5%, or is there some turning point where that will start to increase? I'm no expert on this, where in the world are you getting that this is <5% gap? again, 3990WX is an absolute best-case scenario here, that is putting a laptop Apple chip up against a HEDT-class (really, server-class) CPU with 6 times the silicon area and five times the TDP, and all it can do is match it. Mac Pro is the Apple competitor to those chips, and you'll see it slide back into the lead again. and again, task energy as a measurement favors getting it done faster over pure perf/watt. It's still a 280W TDP / 350W PPT chip against a 60W laptop chip, and it has way more silicon, it's the best case scenario and all they can do is match the M1 in task energy. That's actually still an extremely good outcome for the M1 and the 40-core Mac Pro is going to slide back over the top again.
adfrhgeaq5hy 5y ago
>A factor of 2-to-3 IPC difference? That is irrelevant. What matters is the product of IPC and frequency. x86 parts today are clocked much, much higher than Apple's parts. IPC and frequency are both means to an end. Compare on performance and efficiency, not implementation details.
- paulmd 5y ago
  It is very relevant: people keep bringing up the "x86 loses because it is clocked higher" (you did so yourself!) but the thing is, sure, clock that x86 down and then instead of matching in performance and losing heavily in perf/watt you lose heavily in performance and match in perf/watt. The fact of the matter here is that Apple is getting much better IPC at a much better power-per-core, and that is the real architectural gap. You can slide around where on the scale that x86 falls, but there isn't enough gain from a full node shrink to close a factor-of-6 perf/watt gap and a 3x IPC gap.
  - adfrhgeaq5hy 5y ago
    CPUs are designed to hit a certain clock rate. The target frequency influences the design of literally every circuit in the CPU. Downclocking a CPU is not the same as designing it for a lower frequency. An x86 CPU is designed to run at ~5GHz in its highest turbo mode. Simply reducing the frequency in the BIOS does not undo all the tradeoffs the architects made that deliberately sacrificed IPC for frequency. You could make a very wide CPU indeed if you decided to run it at 100MHz. That would be obviously stupid, though, because it is the product of IPC and frequency that matters. It certainly looks like Apple has made the better tradeoff. However, you can only tell that from the benchmarks. Either going wider or going faster are valid approaches.
    - paulmd 5y ago
      This of course has the subtle implication that it’s equally easy for x86 to go as wide as ARM, and it’s not. Yes, it’s true that x86 often relaxes pitch, that doesn’t make up for a factor of 6 perf/watt difference like Anandtech measures. Like I said, I guess we’ll see, Zen4 and A16 will be on the same node next year. By that time the goalpost will move to something else, like this “x86 isn’t designed for power efficiency” defense.

by paulmd 5y ago

TomVDB 5y ago

> Does anyone expect x86 to close a factor-of-6 perf/watt difference? The one number that surprised me in this review was that the perf/W of Threadripper for the rendering phase: it is very close to the M1 Max. I understand that the numbers are not apples to apples because of the total laptop vs CPU-only comparison, but the power consumption of the Threadripper CPU itself is very high and probably takes the lion's share of the overall power consumption. And that's for a previous generation Threadripper.

paulmd 5y ago
task energy comparisons are usually won by the processor that gets it done fastest in absolute terms: because of the overhead of the rest of the system, it takes a really big perf/watt win to come out ahead of the system that maybe isn't as efficient in actual watts but gets it done in half the time, because you pay the system overhead for a shorter period of time. it's also a 128-thread processor being put against a 8+2 thread processor, and that's the closest thing to something that will outweigh Apple's IPC advantage here: super wide processor clocked super slow, and unlike the more realistic comparisons (laptop processors, etc) the Epyc has deployed over four times as much silicon just to match the M1. This is the absolute best-case scenario for x86 - they get six times as much silicon and 16 times as many threads and all they can do is match it. Do the comparison again against the Mac Pro 40-core chip when it comes out and you'll see A15 pull ahead again.
- nathanielarmer 5y ago
  I think you're getting a bit confused. The 3990x is not designed for energy efficiency, on an older node, and on an older architecture... uses 3kWh vs Apples 2kWh (using a very flawed methodology). An yet you're claiming Apple has a 3-6x power efficiency advantage. I'm not sure how that makes any sense.
  - paulmd 5y ago
    Hmm? Perf/watt isn’t the same thing as task energy, it sounds like you’re the one confused here. As I said, task energy (which is what’s measured in the OP) heavily favors “getting it done quicker” as well as this task being embarrassingly parallel such that the 3990WX can get all 128 threads into play. It’s basically a “race to sleep” benchmark not a perf/watt benchmark with processors that are that disparate. For a task energy test - which is not the same thing as a perf/watt test - this is completely loading the dice in favor of x86 and M1 still manages to match it. That is an extremely good result for putting a laptop chip against a top of the line HEDT processor in a test that is normally all about race to sleep. > An yet you're claiming Apple has a 3-6x power efficiency advantage. I’m not the one claiming anything, if you disagree with Anandtech’s numbers go take it up with them. The numbers don’t change just because you find them uncomfortable. > In multi-threaded tests, the 11980HK is clearly allowed to go to much higher power levels than the M1 Max, reaching package power levels of 80W, for 105-110W active wall power, significantly more than what the MacBook Pro here is drawing. The performance levels of the M1 Max are significantly higher than the Intel chip here, due to the much better scalability of the cores. The perf/W differences here are 4-6x in favour of the M1 Max, all whilst posting significantly better performance, meaning the perf/W at ISO-perf would be even higher than this. > In the SPECfp suite, the M1 Max is in its own category of silicon with no comparison in the market. It completely demolishes any laptop contender, showcasing 2.2x performance of the second-best laptop chip. The M1 Max even manages to outperform the 16-core 5950X – a chip whose package power is at 142W, with rest of system even quite above that. It’s an absolutely absurd comparison and a situation we haven’t seen the likes of. https://www.anandtech.com/show/17024/apple-m1-max-performance-review/3 https://www.anandtech.com/show/17024/apple-m1-max-performanc... And again, that’s with it running at half the clock and half the threads of its laptop peers, so IPC is something like 8x higher in those scenarios. That is not the kind of gap you close up with a node shrink or tightening pitches a bit. Hackernews experts know best though. Next year Zen4 and A16 will be on the same node, and then it’ll be another excuse for why x86 is still getting dumpstered. Just keep the goalposts on wheels, you’ll need it.

throwawaylinux 5y ago

I don't really know where to start on this. SKUs that target very different markets are necessarily going to have different performance and efficiency tradeoffs. And core which target different cycle times are going to be able to achieve different IPC. This clearly confuses the basis of performance and different freq/ipc design points. I also didn't suggest Apple would never have the best chips ever. Clearly all else being equal if ISA was irrelevant and you had 1 ARM competitor and 1 x86 competitor then sometimes the ARM CPU is going to be the better of the two. I'm asking is there some continued effect by which people think ARM is going to continue to pull ahead. Is it going to remain < 5%, or is there some turning point where that will start to increase? I'm no expert on this, but there are experts who don't seem to think that there will be such an inflection point.

paulmd 5y ago
> I don't really know where to start on this. SKUs that target very different markets are necessarily going to have different performance and efficiency tradeoffs. And core which target different cycle times are going to be able to achieve different IPC. This clearly confuses the basis of performance and different freq/ipc design points. see my response elsewhere, but these aren't unrelated problems: Apple has higher IPC at a lower power-per-core. You can slide around where on the scale x86 falls - maybe you can match perf/watt but then you're getting wiped by a factor of 3 on performance, and you can match on performance but then you're getting wiped by a factor of 6 on perf-watt. You can't do both at once. There simply isn't enough transistor gain from a single node shrink there to clear that much of a gap, basically Apple is also seeing much better performance-per-transistor and that's a harder gap to close. > I'm asking is there some continued effect by which people think ARM is going to continue to pull ahead. Is it going to remain < 5%, or is there some turning point where that will start to increase? I'm no expert on this, where in the world are you getting that this is <5% gap? again, 3990WX is an absolute best-case scenario here, that is putting a laptop Apple chip up against a HEDT-class (really, server-class) CPU with 6 times the silicon area and five times the TDP, and all it can do is match it. Mac Pro is the Apple competitor to those chips, and you'll see it slide back into the lead again. and again, task energy as a measurement favors getting it done faster over pure perf/watt. It's still a 280W TDP / 350W PPT chip against a 60W laptop chip, and it has way more silicon, it's the best case scenario and all they can do is match the M1 in task energy. That's actually still an extremely good outcome for the M1 and the 40-core Mac Pro is going to slide back over the top again.

adfrhgeaq5hy 5y ago

>A factor of 2-to-3 IPC difference? That is irrelevant. What matters is the product of IPC and frequency. x86 parts today are clocked much, much higher than Apple's parts. IPC and frequency are both means to an end. Compare on performance and efficiency, not implementation details.

paulmd 5y ago
It is very relevant: people keep bringing up the "x86 loses because it is clocked higher" (you did so yourself!) but the thing is, sure, clock that x86 down and then instead of matching in performance and losing heavily in perf/watt you lose heavily in performance and match in perf/watt. The fact of the matter here is that Apple is getting much better IPC at a much better power-per-core, and that is the real architectural gap. You can slide around where on the scale that x86 falls, but there isn't enough gain from a full node shrink to close a factor-of-6 perf/watt gap and a 3x IPC gap.
- adfrhgeaq5hy 5y ago
  CPUs are designed to hit a certain clock rate. The target frequency influences the design of literally every circuit in the CPU. Downclocking a CPU is not the same as designing it for a lower frequency. An x86 CPU is designed to run at ~5GHz in its highest turbo mode. Simply reducing the frequency in the BIOS does not undo all the tradeoffs the architects made that deliberately sacrificed IPC for frequency. You could make a very wide CPU indeed if you decided to run it at 100MHz. That would be obviously stupid, though, because it is the product of IPC and frequency that matters. It certainly looks like Apple has made the better tradeoff. However, you can only tell that from the benchmarks. Either going wider or going faster are valid approaches.
  - paulmd 5y ago
    This of course has the subtle implication that it’s equally easy for x86 to go as wide as ARM, and it’s not. Yes, it’s true that x86 often relaxes pitch, that doesn’t make up for a factor of 6 perf/watt difference like Anandtech measures. Like I said, I guess we’ll see, Zen4 and A16 will be on the same node next year. By that time the goalpost will move to something else, like this “x86 isn’t designed for power efficiency” defense.