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Apple Silicon Mac Pro uses PCIe switches to support all slots

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

#61

Post by varispeed »

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.

> just without consideration for constraints imposed by the phone's footprint

If you don't have those constraints it is easy to just "copy and paste" more cores and naturally this will have a higher power envelope, but in essence this is a phone tech that you pay extreme premium for.

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

#62

Post by solardev »

sprash wrote: post #53
ohgodplsno wrote: post #45

Earlier quoted context omitted.

Curious to see how you imagine swapping all the registers and caches of a currently broken CPU (so, unable to do anything including sending those registers somewhere). Because if you don't, sure, you didn't technically power down your machine, you just fucked up your entire stack, stack pointer goes to the wrong place, checks based on hardware are now wrong... In effect, you powered down the machine because your OS w…

The equivalent to flushing your register state is more comparable to a context switch than a complete shut down. Also Thanks to PCIe CPU swapping could be done in pure software at the OS level. No further hardware changes required. Simply copy the contents of your RAM to the other CPU card and manage the hand-off. This is clearly different from a complete shutdown e.g. all devices on the PCIe bus would be able to kee…

As a web developer unfamiliar with the hardware stack, I was surprised by this part...

> A good programmer familiar with the target OS and inner workings of PCIe could deliver a working prototype within a week, production ready within less than a year.

Could you please explain why it'd be normal to take a year to go from prototype to production in this case? What would happen in that one year, starting from a working prototype?

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

#63

Post by detourdog »

c00lio wrote: post #58
detourdog wrote: post #15

Earlier quoted context omitted.

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 shi…

The defining characteristic of PCIe isn't faster bus timings. It is that PCIe isn't even a "bus" in the traditional sense. With a bus, you have a number of shared physical wires for addresses and data, and an arbitration system that assigns those shared wires to one device at a time. The available bandwidth is just the bandwidth of the bus, divided into the time you can reserve it for yourself. PCIe is a tree-shaped…

That sounds like a good description but do you think the term serial should be worked in there?

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

#64

Post by fmajid »

meindnoch wrote: post #29
sprash wrote: post #20

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.

What is exactly the use case for hot-swapping CPUs?

Fault-tolerant systems with five nines uptime requirements.

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

#65

Post by fmajid »

numpad0 wrote: post #48
danpalmer wrote: post #13

Earlier quoted context omitted.

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.

> top end Intel i9 Intel top end is Xeon. i9 is gamer CPU, more or less.

The i9 is used in HP Z2 workstations (with ECC memory) because of the delays to Sapphire Rapids.

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

#66

Post by meindnoch »

trollied wrote: post #40
meindnoch wrote: post #29

Earlier quoted context omitted.

What is exactly the use case for hot-swapping CPUs?

Swapping a failed device for a working one, without powering down the machine.

But why would you do that on a Mac workstation?

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

#67

Post by meindnoch »

fmajid wrote: post #64
meindnoch wrote: post #29

Earlier quoted context omitted.

What is exactly the use case for hot-swapping CPUs?

Fault-tolerant systems with five nines uptime requirements.

How many people would run such fault-tolerant systems on Mac workstations?

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

#68

Post by sprash »

solardev wrote: post #62
sprash wrote: post #53

Earlier quoted context omitted.

The equivalent to flushing your register state is more comparable to a context switch than a complete shut down. Also Thanks to PCIe CPU swapping could be done in pure software at the OS level. No further hardware changes required. Simply copy the contents of your RAM to the other CPU card and manage the hand-off. This is clearly different from a complete shutdown e.g. all devices on the PCIe bus would be able to kee…

As a web developer unfamiliar with the hardware stack, I was surprised by this part... > A good programmer familiar with the target OS and inner workings of PCIe could deliver a working prototype within a week, production ready within less than a year. Could you please explain why it'd be normal to take a year to go from prototype to production in this case? What would happen in that one year, starting from a working…

Most of the time will be spend on undocumented corner cases of third party hardware and dealing with various race conditions. Even though the PCIe protocol is reasonably simple the devices attached to it are not. Since this feature is only viable if it works 100% reliable the rule of thumb is the last 20% of problems will cost you 80% of the time.

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

#69

Post by wkat4242 »

detourdog wrote: post #25
wkat4242 wrote: post #6

Earlier quoted context omitted.

Of course Apple positions this as a proper workstation.

Why wouldn't they? If a Sun Blade 100 is a workstation and I can do the same tasks faster on a Mac mini or Mac Pro why wouldn't they be workstations. Don't get too hung up on labels they can distract from what is front of you. If Apple Silicon actually is an entire motherboard shrunk to die size the shrunken die motherboard will be faster. Place that chip onto a larger motherboard and you get real efficiencies that a…

Well, workstation implies a lot. And the price. It's not just a marketing term. It implies more PCIe lanes than a normal desktop (which in this case is not being realised) and better graphics capability for intensive tasks. The latter is up for debate. I'd imagine a 4090 equipped HEDT still kicks its ass in most workstation-type workloads.

The unified memory is great for LLM style tasks of course and it's one of the few ways to get a GPU setup with over 100GB for less than $100k.

PS Not sure how the comparison with a 20 year old system applies though ;)

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

#70

Post by unusualmonkey »

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 memory bus is overblown.

M2 Ultra has 800GB/s, which sounds like a lot until you remember a Xbox Series X has 560GB/s and costs $499. Or spend $800 and get a 7900 XT which has 800GB/s.

Think of the Ultra more of a GPU that happens to have CPU built in.

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