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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

#81

Post by c00lio »

detourdog wrote: post #80
c00lio wrote: post #78

Earlier quoted context omitted.

On some level yes, on some level no. The physical interface for each point-to-point link is serial, but one device can have several of those links and use them (send/receive packets on them) in parallel.

Does the lane count correspond to the quantity of parallel links? would the switches be single transistors?

Yes, lane count is the number of parallel links.

Switches are far more complex. The protocol specifies addressing, bandwidth reservations, flow control, priorities and message ordering requirements, which the switches have to handle.

Not a switch thing per se, but also relevant for "single transistors won't do": On the physical layer, each port/link is also relatively complicated to initialize and operate. The transmission encoding, due to the relatively high speeds involved, requires a learning phase where both ends measure the link characteristics and adjust their (relatively complex) signal processing accordingly. The physical layer also handles different link speeds for down-/upward compatibility.

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

#82

Post by detourdog »

detourdog wrote: post #80
c00lio wrote: post #78

Earlier quoted context omitted.

On some level yes, on some level no. The physical interface for each point-to-point link is serial, but one device can have several of those links and use them (send/receive packets on them) in parallel.

Does the lane count correspond to the quantity of parallel links? would the switches be single transistors?

This sounds like an ideal config for unified memory. I suppose that one can count all the lanes to figure out the actually total throughput. Does every vendor come up with their own implementation of a "busmaster"?

This may explains how they achieve the graphics blitting in the Vision Pro.

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

#83

Post by detourdog »

nottorp wrote: post #44
teruakohatu wrote: post #2

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

Well mac os doesnt support non Apple gpus any more. And if you want to run Linux with a bunch of compute GPUs Im sure there are more appropriate solutions than Apple hardware. Not sure how this affects the use case of multiple video capture cards writing to fast internal storage that I see mentioned here and there. Anyone close to that industry around to comment? Edit: i think I’ve seen mentioned that the PSU in this…

If one looks at all the encode/decode streams that Apple claims happen on processor I wonder how significant this is.

The graphics and processing speed of the Vision Pro makes me wonder if the GPUs are truly needed.

Most of the cards for the M2 Mac Pro are used to access the analog world. It seems that there is power inside the die and if you need an analog signal use a PCI-e port.

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

#84

Post by nottorp »

detourdog wrote: post #83
nottorp wrote: post #44

Earlier quoted context omitted.

Well mac os doesnt support non Apple gpus any more. And if you want to run Linux with a bunch of compute GPUs Im sure there are more appropriate solutions than Apple hardware. Not sure how this affects the use case of multiple video capture cards writing to fast internal storage that I see mentioned here and there. Anyone close to that industry around to comment? Edit: i think I’ve seen mentioned that the PSU in this…

If one looks at all the encode/decode streams that Apple claims happen on processor I wonder how significant this is. The graphics and processing speed of the Vision Pro makes me wonder if the GPUs are truly needed. Most of the cards for the M2 Mac Pro are used to access the analog world. It seems that there is power inside the die and if you need an analog signal use a PCI-e port.

It's probably good or even powerful for professional video editing.

For GPU compute, I'm sure it can't beat 15 kW of nvidia dedicated cards.

But then you don't want 15 kW of cooling on your desk.

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

#85

Post by detourdog »

nottorp wrote: post #84
detourdog wrote: post #83

Earlier quoted context omitted.

If one looks at all the encode/decode streams that Apple claims happen on processor I wonder how significant this is. The graphics and processing speed of the Vision Pro makes me wonder if the GPUs are truly needed. Most of the cards for the M2 Mac Pro are used to access the analog world. It seems that there is power inside the die and if you need an analog signal use a PCI-e port.

It's probably good or even powerful for professional video editing. For GPU compute, I'm sure it can't beat 15 kW of nvidia dedicated cards. But then you don't want 15 kW of cooling on your desk.

Where I get confused is what is the extra kW doing? It has been at least a decade since I did any intense projects but doesn't 15kW represent the power of an average American household circuit. The entire Mac Pro only supports 3 8k displays with built-in hardware. One would need to add SDI cards to add extra displays but the computer only draws 300 Watts. I could get 50 Mac Pros and give up which would give 150 8k displays without expansion. Maybe one gives up the convenience of a single card solution but there maybe other advantages.

I'm mostly curious as to what this work load consists of?

but when I read the number 8k encode and decode streams 15 kW represents

How much of the power is just getting the data in and out of the card to the processor. Apple Silicon doing the same work on die is going to use less power. I don't doubt that there are faster processing units.

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