programmer

Marvin said:

Apple's tile-based GPU refers to the way it renders images, not the way the physical chips are structured:

https://developer.apple.com/documentation/metal/tailor_your_apps_for_apple_gpus_and_tile-based_deferred_rendering
https://www.rastergrid.com/blog/gpu-tech/2021/07/gpu-architecture-types-explained/

AMD GPUs use physical chiplets but they use immediate mode rendering rather than tile-based rendering.

This means that GPU drivers have to accommodate each rendering architecture. If Apple writes the drivers, they have to maintain both.

They've already done this as Metal software runs ok on AMD GPUs. In the Blender Metal features, Apple added support for AMD and Intel:

https://developer.blender.org/T92212

They have an active install base over 100m who still have Intel/AMD and this will be the case for a few years.

Marvin beat me to it.  Great answer, with reference links to back it up!  Thanks.

While Apple is currently stuck supporting immediate mode rendering architecture, eventually they won't be... if they stop building new hardware that uses it.  And they can start adding new features which only support their preferred (tile-based) rendering architecture much sooner than that.  As soon as all the Intel and AMD chips are gone from their models currently on sale, their software people can move to a model where new graphics functionality might be "Apple Silicon only".  That's a harder sell if they're still selling Intel/AMD based hardware. 

I haven't seen it mentioned here that there is a fundamental architectural difference between the Apple Silicon GPU and pretty much every other GPU architecture (except Imagination/PowerVR):  it is a tile-based architecture.  If you look at the Metal programming manual, there are numerous differences in how the two types of architectures need to be dealt with by the application.  Those differences will be even more severe at the OS/driver level.  Apple is quite aggressive at dropping old hardware in order to reduce their software burden (given, as mentioned above, software lifecycles are actually longer than hardware delivery cycles), and I would imagine they want to get to a place where (in Metal 4 or 5) they can completely focus on their hardware's tile-based architecture, and not have to accommodate AMD/nVidia designs.  Same applies to the rumoured "ray tracing" support -- they'll want to do it their way, and will ship it once they get the design working (maybe M3, as clearly missed the shipping schedule in 2022).

The problem, of course, is that most of their market is in mobile devices and consumer computers.  So scaling to the workstation level is going to take a back seat, or at least have to make do with however well it scales.  In the M1 generation, if obviously didn't scale well enough to ship a Mac Pro.  Enough time has passed now that the market pressure for a Mac Pro means they're going to have to give it a go on the M2.  It is unlikely to live up to everyone's expectations.

As others have observed above, I expect to see PCIe slots in the Mac Pro.  The Apple Silicon supports it for Thunderbolt 4.  What kinds of devices it can support will depend on which version they implement, how much power delivery they provide, and (most importantly) the device drivers.  Due to the architectural differences described above, I am not expecting to see GPUs from other vendors supported as display devices.  The market to use GPU cards as non-display devices (e.g. ML or other compute acceleration) is small and not interesting for Apple nor nVidia to support, so I doubt anyone will do the necessary driver development... but the hardware ought to function, so conceivably someone could do an open source driver (for non-display uses).  That's very niche though, so not holding my breath except as a cool demo.  Other kinds of PCIe cards will mostly be up to the card vendors to supply drivers for, and that will be similar to past Mac Pro support levels (porting those to Apple Silicon shouldn't be too painful for the devs).

Memory expandability is another tricky issue.  While the chips they're embedding in their M1/M2 packaging are standard memory chips, they've not had to deal with the challenges of longer traces that go out to the motherboard and to DIMMs of varying quality.  So I'm doubtful they will switch to motherboard-based DIMMs in the Mac Pro.  Other strategies to get to large memory sizes are possible, particularly with OS support, but my guess is that they'll just live with whatever their M2 Ultra can manage -- not likely to exceed 128GB.  A PCIe RAM board as VM swap store, with minimal software support required, could offer an option to users who need huge memory footprints, but there is obviously an efficiency loss there.  Without a more sophisticated chip interconnect though, there aren't really many options open to Apple Silicon (yet)...

The Ultra's edge interconnect allowed 2 M1 Max chips to connect.  Scaling that to more than 2 chips is non-trivial because high performance interconnects like that are very very sensitive to trace lengths, cross-talk noise between wires, etc.  Who knows what they've done in terms of the protocol across this interconnect though, their approach may support a different hardware implementation that could handle an interposer or perhaps 2 edges on a single chip.  Chip edge real estate is precious though -- you only get 4 of edges, and in the M1/M2 two of those edges are very busy providing the memory and I/O connections.  So perhaps they could have connectors on either end and go to 3 chips?  Or accept the inevitable latencies involved in an interposer/switch of some kind (not to mention how hard it is to build such a thing) and enable going to more "chiplets" including 3D stacking options?  Cramming all this physically in the same package gets tough and the manufacturing tech for doing this is still really expensive, so is Apple going to try and pioneer such a thing only for a very high end low volume product like the Mac Pro?  I'm doubtful they will at this stage... right now I think they need to get a low-risk Apple Silicon Mac Pro into the market with as much expandability as they can manage right now.  That won't be enough for everyone (nothing ever is), but it'll satisfy some of the market.  Going forward, this sort of chiplet-based fabric approach will become more mainstream and will make more sense for Apple to adopt across more of its product line, and that may give them better scaling opportunities at the Mac Pro end of the product line.

So I think that, while the upcoming Mac Pro may not hit all the check boxes you'd like, that doesn't mean it is doomed going forward, and doesn't mean it won't find a worthwhile enough market.  Apple went through the 2013 Mac Pro fiasco, so they're aware of what the Mac Pro demand really is, they just may not be able to fully achieve it on this iteration.  They're late on their "two years to all Apple Silicon" promise (partly blamed on the pandemic), so no doubt they want to get something out there so they can stop supporting Intel chips ASAP.  

FileMakerFeller said:

bulk001 said:

So what’s it been? A year or two and Apple is already basically at the same place Intel is with Incremental updates spread out over a period of years unable to deliver on a predictable timetable. Yes there are some battery life advantages and the initial jump of the v1 chip but it is not very promising moving forward if this is accurate! 

... while dealing with the massive disruption brought about by a global pandemic. I don't share your pessimism. Remember that Apple famously ships a great v1.0 and then iterates consistently; some people moan about the lack of regular "OMG" updates but over time the consistency of improvement leads to massive gains.

Also, tenthousandthings pointed out that in 2014 (a mere 8 years ago!) TSMC was using a 20nm process node. I mentally used a swear word when I read that. Astonishing progress to be shipping at 5nm and imminently 3nm in that timeframe. Well done to everyone at TSMC, that is spectacular!

A resetting of expectations is also required.  The reality of semiconductor fabrication is that since running into the power wall back in the mid-00s, things haven't been scaling smoothly like they had since humanity started building integrated circuits.  The time between nodes has increased, the risk of going to new nodes has increased, and the cost of going to new nodes has dramatically increased.  The free lunch ended almost two decades ago, and since then the semiconductor industry has been clawing out improvements with higher effort and lower rewards. A lot of the improvements that have been gained has happened by doing things other than simply bumping CPU clock rate and cache sizes.  GPU advancements were the first "post-CPU" wave, SoC happened in the mobile space first then moved into the laptop/desktop space, and more recently ML related hardware has become common.  Most of these things require software changes to make any use of at all, nevermind actually optimizing for them.  And that is why Apple needed to move to Apple Silicon -- not because they could build a better CPU than Intel, but because they need to build the chip Apple needs.  There is far more in the Axx/Mx chips than just the CPUs and GPUs.  How they are interconnected, how they share cache/memory resources, fixed function hardware units, what is the mix of devices, how the various accelerators are tuned for the workloads running on Apple systems, etc.  Expect to see variants tuned for specific systems, perhaps variants at the packaging level... the same cores re-packaged and used in different configurations, etc.

Just the fact that TSMC has so many variations on the 5nm process node ought to be a clue about how hard getting to the next level has become.  Intel being stuck for a long time at 10nm was a foreshadowing of the future.  And at each stage, the designers are going to have to work harder and innovate more with each process advancement to wring as much value from it as possible... because the next one is going to be even more horrendously expensive and risky (and likely bring diminishing returns, plus "interesting" problems).

Fred257 said:

I’m not getting near any M2 anything. The reviews I have seen show absolutely no consistency in both the CPU and GPU reviews. As a matter of fact I think it’s the worst Apple architecture we will see. Apple, fix your stupid mistakes!! Only one NAND chip on the lower end models is a complete design flaw and ultra cheap on your part. The GPU being slower on the 10 core then the 8 is inexcusable!! Stop and improve these mistakes please. And for Apple fanboys here who complain about me I’ve used Macs since 1989 making music on Cubase before many of you were in your mothers womb 

I think this is a confluence of a couple of things.  Their low end machines are using a single NAND chip as a cost saving measure, and the higher end machines shouldn't do that.  The GPU being slower on 10 vs 8 cores is likely a software thing (in the driver or Metal) or a benchmarking artifact.

As usual, you need to assess the machine you're interested in (when that becomes possible), not projections or theorizing about what it'll be.  I think the M2 pro/max/ultra/whatever are going to be pretty impressive chips and Apple will put them in either the same or improved systems compared to last year's models.  Hopefully the long awaited Mac Pro arrives too.

It looks like their single-core plot is using their projected performance estimates for the presumed M2 Pro, M2 Max and M2 Ultra.  See the thread on the Future Hardware forum.