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Apple Silicon Mac Pro uses PCIe switches to support all slots

social.treehouse.systems

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Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#11

Post by daneel_w »

varispeed wrote: post #9
wkat4242 wrote: post #6

Earlier quoted context omitted.

Of course Apple positions this as a proper workstation.

I remember being downvoted for saying this is essentially a phone CPU and motherboard, just without consideration for constraints imposed by the phone's footprint. It means it can be designed with higher TDP in mind etc. and yet, Apple charges for it as if it was a real workstation equipment rather than a phone in a massive enclosure.

Why is it "essentially" a phone CPU? Please don't say "because of the ISA". It has 24 CPU cores, 60+ GPU cores, an insanely fast memory bus and a purported 60 watt power envelope. There's nothing "phone" about it.

Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#12

Post by martini333 »

varispeed wrote: post #9
wkat4242 wrote: post #6

Earlier quoted context omitted.

Of course Apple positions this as a proper workstation.

I remember being downvoted for saying this is essentially a phone CPU and motherboard, just without consideration for constraints imposed by the phone's footprint. It means it can be designed with higher TDP in mind etc. and yet, Apple charges for it as if it was a real workstation equipment rather than a phone in a massive enclosure.

Do you think there is only phone CPU's and real workstation CPU's? Nothing in-between? If so, I get why you got downvoted.

Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#13

Post by danpalmer »

c00lio wrote: post #3

Apple Silicon is low-power low-end laptop hardware. Of course their I/O capabilities are limited, because their users do not need lots of I/O. If you are looking for stuff with lots of I/O capabilities you have to buy proper server hardware.

Not defending the Mac Pro's architecture here, I think there are issues, but calling Apple Silicon "low-end laptop hardware" is just false. The Max/Ultra chips easily outperform most server-grade CPUs, and are similar to top end Intel i9 chips. Then if you also take into account performance per watt, they're in a whole different league.

Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#15

Post by detourdog »

rerx wrote: post #4
teruakohatu wrote: post #2

What is the consequence of this? Does it limit the theoretical ability to add GPUs?

If you add multiple GPUs to the same PCIe switch, their bandwidth to main memory of the SOC will be shared. For some use cases that bandwidth was already the bottle neck.

Using the older PCI bus every three or 4 slots represented a dedicated controller. We would install the high bandwidth cards on seperate controllers. PCI-E exists in a faster timing bus which may make a difference. The visionOS demo apparently shows sub 20 nanosecond processing and graphics blitting to appear imperceptibly.

Finally Woz’s design for the Apple II color graphics was based on unified memory.

Dramatic shifts in technology sometimes obviates all our past learning and experience.

Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#16

Post by microtonal »

daneel_w wrote: post #11
varispeed wrote: post #9

Earlier quoted context omitted.

I remember being downvoted for saying this is essentially a phone CPU and motherboard, just without consideration for constraints imposed by the phone's footprint. It means it can be designed with higher TDP in mind etc. and yet, Apple charges for it as if it was a real workstation equipment rather than a phone in a massive enclosure.

Why is it "essentially" a phone CPU? Please don't say "because of the ISA". It has 24 CPU cores, 60+ GPU cores, an insanely fast memory bus and a purported 60 watt power envelope. There's nothing "phone" about it.

And Thunderbolt. Show me all those phones with Thunderbolt :).

Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#17

Post by phire »

c00lio wrote: post #7
teruakohatu wrote: post #2

What is the consequence of this? Does it limit the theoretical ability to add GPUs?

Actually, no. It only limits the available I/O bandwidth to those GPU(s), that is, data transfers from and to the CPU will be far slower. You'll notice in games when the "loading next level" screen takes longer, that's usually a large geometry and texture copy to the GPU. As an extreme example, when and where it was/is still viable, cryptocurrency mining operations use external PCIe cases with lots of slots, attached…

In the case of multi-gpu gaming, loading might not be an issue.

You are sending the exact same data to both GPUs. If the the PCIe switch and GPU drivers support multicast, then you would actually get the full 16x bandwidth to both.

Which is actually a huge advantage over the most common multi-gpu setup, which is forced to statically split the 16 PCIe lanes into two independent 8x slots. Even if you were playing a game that only used one GPU, simply having the second gpu plugged in meant your total bandwidth to each gpu was limited to 8x speed.

I really wish you could find x86 motherboards with PCIe switch chips... but switch chips are really expensive so nobody makes them.

Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#18

Post by ddalex »

daneel_w wrote: post #11
varispeed wrote: post #9

Earlier quoted context omitted.

I remember being downvoted for saying this is essentially a phone CPU and motherboard, just without consideration for constraints imposed by the phone's footprint. It means it can be designed with higher TDP in mind etc. and yet, Apple charges for it as if it was a real workstation equipment rather than a phone in a massive enclosure.

Why is it "essentially" a phone CPU? Please don't say "because of the ISA". It has 24 CPU cores, 60+ GPU cores, an insanely fast memory bus and a purported 60 watt power envelope. There's nothing "phone" about it.

the 60W envelope is the phone part

I mean you can't style yourself a workstation if the lights don't dim when turned on

Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#19

Post by dhruvdh »

daneel_w wrote: post #11
varispeed wrote: post #9

Earlier quoted context omitted.

I remember being downvoted for saying this is essentially a phone CPU and motherboard, just without consideration for constraints imposed by the phone's footprint. It means it can be designed with higher TDP in mind etc. and yet, Apple charges for it as if it was a real workstation equipment rather than a phone in a massive enclosure.

Why is it "essentially" a phone CPU? Please don't say "because of the ISA". It has 24 CPU cores, 60+ GPU cores, an insanely fast memory bus and a purported 60 watt power envelope. There's nothing "phone" about it.

All fabs have libraries that their customers use to turn chip RTL to actual transistor layout to be fabbed.

Apple silicon is made using mobile libraries, same as their iPhone and iPad chips. Even though they're made on these dense libraries, the chip is still very big, since they need to include CPUs, GPUs, NPUs, and all of their fixed function hardware.

All of this puts a limit in terms of frequency and core count. You will find that other server hardware in this price range significantly outperforms Apple silicon , save for those video workloads they're missing fixed function hardware for.

M2 Ultra has some 134B transistors, when you compare with an equivalent chip like MI300 (146B), you find that really, in terms of raw compute, there is no comparison. We will have more details on MI300 today, watch out for the news cycle.

This is an excellent read in terms of what difference using dense vs performance libraries can make - https://www.semianalysis.com/p/zen-4c-amds-response-to-hyper...

Re: Apple Silicon Mac Pro uses PCIe switches to support all slots

#20

Post by sprash »

If you have switched PCIe anyways I would have loved a Mac Pro with a "passive" switched PCIe backplane where you can hotplug PCIe devices in including M2 CPU PCIe cards. Also polish the OS accordingly that you can upgrade/switch your CPU in live operations without shutting down the OS or may be even run Apple silicon CPUs and x86 CPUs alongside.
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