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Apple already outclasses everyone in throughput & throughput/watt especially. In case it wasn't already crystal clear, I was talking about everyone else finding

Apple already outclasses everyone in throughput & throughput/watt especially. In case it wasn't already crystal clear, I was talking about everyone else finding ways to get their throughput up to more competitive levels, such as by supporting GDDR.

dathinab 3y ago
But a huge part of their throughput numbers is them having the equivalent of 16 memory channels. AFIK it's not that e.g. AMD couldn't do that and use on-die LPDDR5, I mean that is a bit different but not sustainable harder then using their chiplet + X3D tech. The problem is that for AMD it's not a good business decision. First they need to be price competitive (a problem Apple doesn't have). Most applications outside some areas scale much more with the speed/latency of RAM then with bandwidth increase (beyond some basic level). In turn for a lot of e.g. desktop Ryzen processor use cases which are not media processing there is not enough value into adding many more channels. Especially if you consider that for large parts of the prosumer/server space IT admins will be really unhappy with on-die RAM Apple can afford forcing it, AMD can not. The reason is that while for desktop systems RAM death is rarely an issue in the server/heavily used workstation spectrum RAM death is not uncommon. Even for media processing or multi VM servers going beyond a certain number of channels (less then 16) is unlikely to be a good financial decision. I would go as far as arguing if the M2 Ultra wouldn't be based on tightly gluing 2 processors together and that processors have 8 channels because they are sold with a focus for media processing it wouldn't have anywhere close to 16 channels (but for Apple the cost of having less then 16 channels with their design is higher then the cost of having them, partially because they also don't sell server they don't want to compete with accidentally and similar). Where I'm going with this is that outside of some media processing targeted products they don't need to "get their throughput up to more competive level" and getting it to having a some additional 8 channel choices (e.g. for some high end laptops) would likely be good enough in practice. And in turn we are unlikely to see more. And in turn they have no reason to try tricks like using GDDR memory. The way Apple can push hardware vendors here is less because of a need for many more channels, but because for a want.
- rektide 3y ago
  I don't know but I could see the possibility that maybe AMD really can use more throughput for mobile chips. To spitball some figures, the rx7600 is 13b transistors, 165watts, and runs off 128-bit 288GBps GDDR6 memory. Or take 2017's rx580, but which was 256-bit GDDR5 good for 224GBps, at similar power. An APU is going to be considerably lower power than either of these discrete gpus. I think I somewhat overestimated AMD's ability to scale up their APUs to be throughput limited, in most cases. The 256GBps LPDDR5X memory they're planning should offer a nice bump over where we are be pretty good. I'm a bit surprised to see the memory bandwidth not being as constraining a factor as I had first guessed. It's also seemingly bizarre how overbuilt it makes Apple's memory setup look.
  - dathinab 3y ago
    I mean it is a constraining factor for live on-the fly real time multi 8k-track video editing and similar ;=) It's just that most people don't do that on a daily usage basis. Maybe not a I need 800GiB/s constraining factor but definitely a I don't want just 200GiB/s constraining factor AFIK.
- sliken 3y ago
  > The problem is that for AMD it's not a good business decision. The PS5 and XboxX have an AMD APU (CPU+IGPU) with a wide memory interface. Seems like a fine decision. What surprises me is they haven't brought it to low/medium range desktops, until Strix Halo in 2024.

dathinab 3y ago

But a huge part of their throughput numbers is them having the equivalent of 16 memory channels. AFIK it's not that e.g. AMD couldn't do that and use on-die LPDDR5, I mean that is a bit different but not sustainable harder then using their chiplet + X3D tech. The problem is that for AMD it's not a good business decision. First they need to be price competitive (a problem Apple doesn't have). Most applications outside some areas scale much more with the speed/latency of RAM then with bandwidth increase (beyond some basic level). In turn for a lot of e.g. desktop Ryzen processor use cases which are not media processing there is not enough value into adding many more channels. Especially if you consider that for large parts of the prosumer/server space IT admins will be really unhappy with on-die RAM Apple can afford forcing it, AMD can not. The reason is that while for desktop systems RAM death is rarely an issue in the server/heavily used workstation spectrum RAM death is not uncommon. Even for media processing or multi VM servers going beyond a certain number of channels (less then 16) is unlikely to be a good financial decision. I would go as far as arguing if the M2 Ultra wouldn't be based on tightly gluing 2 processors together and that processors have 8 channels because they are sold with a focus for media processing it wouldn't have anywhere close to 16 channels (but for Apple the cost of having less then 16 channels with their design is higher then the cost of having them, partially because they also don't sell server they don't want to compete with accidentally and similar). Where I'm going with this is that outside of some media processing targeted products they don't need to "get their throughput up to more competive level" and getting it to having a some additional 8 channel choices (e.g. for some high end laptops) would likely be good enough in practice. And in turn we are unlikely to see more. And in turn they have no reason to try tricks like using GDDR memory. The way Apple can push hardware vendors here is less because of a need for many more channels, but because for a want.

rektide 3y ago
I don't know but I could see the possibility that maybe AMD really can use more throughput for mobile chips. To spitball some figures, the rx7600 is 13b transistors, 165watts, and runs off 128-bit 288GBps GDDR6 memory. Or take 2017's rx580, but which was 256-bit GDDR5 good for 224GBps, at similar power. An APU is going to be considerably lower power than either of these discrete gpus. I think I somewhat overestimated AMD's ability to scale up their APUs to be throughput limited, in most cases. The 256GBps LPDDR5X memory they're planning should offer a nice bump over where we are be pretty good. I'm a bit surprised to see the memory bandwidth not being as constraining a factor as I had first guessed. It's also seemingly bizarre how overbuilt it makes Apple's memory setup look.
- dathinab 3y ago
  I mean it is a constraining factor for live on-the fly real time multi 8k-track video editing and similar ;=) It's just that most people don't do that on a daily usage basis. Maybe not a I need 800GiB/s constraining factor but definitely a I don't want just 200GiB/s constraining factor AFIK.
sliken 3y ago
> The problem is that for AMD it's not a good business decision. The PS5 and XboxX have an AMD APU (CPU+IGPU) with a wide memory interface. Seems like a fine decision. What surprises me is they haven't brought it to low/medium range desktops, until Strix Halo in 2024.