Speculation: Zen 4 (EPYC 4 "Genoa", Ryzen 7000, etc.)

[lobz]

Yes but peak throughput means very little without utilization. Intel went to 356 for the regfile and IPC stayed lower than Zen3, so...
If any, the fact AMD stayed conservative with Zen3 while achieving a significant IPC increase points to many "low hanging fruits" that can be improved in Zen4...

I mean... that's exactly what he's talking about?

 

[leoneazzurro]

I mean... that's exactly what he's talking about?

Yes and no, my point was that Zen3 does indeed improve many things over Zen2, while in the first post it seemed like it was a minor iteration. I never said that it cannot or has not to be improved.

 

[Ajay]

You mean Mike Keller ?

Blast it all. Too bad I wasn't drinking whiskey, I'd blame that.

 

[naukkis]

IIRC it was Papermaster who mentioned about AMD not going with the approach of throwing silicon at the problem and being conservative with die increases for Zen3 to achieve the 19% IPC which is why I am doubting AMD throwing tens of mm2 of die area in cache for questionable lead across the board save for Enterprise loads.

Point was that increasing structure sizes will increase performance but with reduced perf/watt. Increasing cache sizes won't decrease but increase perf/watt.

Intel is at opposite end now, they also did't employ structures that decreased perf/watt previously but they seem to lost it now. They make everything as big as they could and end product is fast at ridiculous power levels, it's pretty much Netburst part two now.

 

[AMDK11]

I didn't even say that, but look at what they changed and how the changed it . Did

peak L/S bandwidth increase , No
peak ALU throughput increase , No
peak FPU throughput increase , No
peak dispatch/issue/retire , No
Peak Decode through increase , No
Number of register file ports , No
Number of FP register file ports , No
Did the floor plan change , No
Did internal structures increase massively in size ( reg ' L/S queue dispatch queue etc) , No
Did the pipeline change , No


Get the point , Zen3 in bound by the Scope of Zen1 and Zen1 was designed with a big enough fundamental base through the core that large gen on gen improvements could happen .

Now compare that list with Willow to Golden or Tremont to Gracemont.

Im saying i think Zen4 wont be bound by the Scope of Zen3. In the same way that Zen wasn't bound by bulldozer yet lots of things came straight from it ( like the FPU still supporting XOP). So i expect fundamental changes in featch/decode , execution and retirement / memory access for Zen 4.

To go to your metaphor go stick a 560HP 6L engine from an enzo in a Golf GTi and see how well it works, there both cars, they both have 4 wheels.

The key part of the microarchitecture is the logic and the algorithms implemented in it that control the core resources. This very key part of the microarchitecture is a closely guarded secret by AMD and Intel. In Zen 3, the logic and algorithms controlling the core resources have been largely replaced by a completely new, more complex one. In Zen2 there was a new such predictor, and in Zen 3 there is a completely new predictor, among others.

 

[LightningZ71]

Point was that increasing structure sizes will increase performance but with reduced perf/watt. Increasing cache sizes won't decrease but increase perf/watt.

Intel is at opposite end now, they also did't employ structures that decreased perf/watt previously but they seem to lost it now. They make everything as big as they could and end product is fast at ridiculous power levels, it's pretty much Netburst part two now.

Having the smaller, high efficiency cores present, Intel doesn't NEED to avoid structures that decrease the performance per watt. If they need to be efficient, they move threads to the Monts. If they need maximum performance, they throw the 5greads at the Coves, power be darned!

 

[A///]

it's pretty much Netburst part two now

I've been saying this for years. Few listen to me, and those who waved my comment off are coming around now. I do not for a second believe Intel will get their power use under control anytime soon, regardless of whatever drivel my life is a disease says.

 

[A///]

Not sure if there was any rumors/confirmation of which team is working on Zen 4, but given that Zen 3 was a ground-up rebuild and Zen 4 also likely to be heavy lift, I would imagine that Zen 3 and Zen 4 are designed by two different teams.

You would be correction with this assumption.

 

[naukkis]

Having the smaller, high efficiency cores present, Intel doesn't NEED to avoid structures that decrease the performance per watt. If they need to be efficient, they move threads to the Monts. If they need maximum performance, they throw the 5greads at the Coves, power be darned!

But what about consequences? They produce huge die which needs expensive motherboards and power supplies to power it - for what, maybe 10% or less more performance than rival designs. That's pure insanity.

 

[moinmoin]

But what about consequences? They produce huge die which needs expensive motherboards and power supplies to power it - for what, maybe 10% or less more performance than rival designs. That's pure insanity.

It is insanity. But it's also the corner Intel itself backed into by having to match the frequencies it achieved on 14nm as well as trying to match the core count of the competition. We need to remember Alder Lake is just the first real reaction to the renewed competitive market environment, still heavily influenced by the years of BK and RS.

 

[LightningZ71]

But what about consequences? They produce huge die which needs expensive motherboards and power supplies to power it - for what, maybe 10% or less more performance than rival designs. That's pure insanity.

What the above poster said, combined with their marketing need to win both single threaded benchmarks AND multi-threaded benchmarks, while having a process and core combination that doesn't allow them to do both of those things with just one core type. It's even harder for them now without the crutch of having an "exclusive" instruction set that enables a handful of big, easy wins to lean on for their composite scores.

 

[xilli_fiberbit]

Some details about 3D V-cache showed by AMD during Hotchips33 :

https://twitter.com/i/web/status/1429470046926123008

AMD on the 3D V-Cache uses 9-micron pitch bonds.

And in the future, even stacking with circuit slicing :

https://twitter.com/i/web/status/1429470841062973447

 

[Mopetar]

Some of that like core-on-core stacking almost seems like it would be infeasible due to issues with heat dissipation. I suppose it could work if you had a very clever layout and employed rotation of some sort so that the problem areas don't overlap or if the clock speeds were intentionally kept low enough where nothing gets too hot, but that does potentially preclude it from some products.

 

[jpiniero]

Some of that like core-on-core stacking almost seems like it would be infeasible due to issues with heat dissipation. I suppose it could work if you had a very clever layout and employed rotation of some sort so that the problem areas don't overlap or if the clock speeds were intentionally kept low enough where nothing gets too hot, but that does potentially preclude it from some products.

You're already getting some of that with GAA.

 

[uzzi38]

All of the biggliest details from the Gigabyte leak for Zen 4:

Details on the Gigabyte Leak

Recently, a ransomware group leaked data from Gigabyte in an attempt to extort payment. That’s been well covered by other outlets (please everyone, secure your networks), so here we’re …

chipsandcheese.com

 

[zir_blazer]

All of the biggliest details from the Gigabyte leak for Zen 4:

Details on the Gigabyte Leak

Recently, a ransomware group leaked data from Gigabyte in an attempt to extort payment. That’s been well covered by other outlets (please everyone, secure your networks), so here we’re …

chipsandcheese.com

The last table, where they are talking about PCIe Lanes per Processor, mentions that Type 1 Model 44h has 2 USB 4 Ports built-in. Type 3 Model 70h too, which I didn't notice before. I don't recall that being mentioned elsewhere.

I wasn't expecting USB 4 support built-in at all. Intel dissapointed me because it will only be included for certain Mobile dies, since the Desktop ones seems to require an external controller. Seems that now both AMD and Intel are at feature parity.

 

[Thibsie]

Some of that like core-on-core stacking almost seems like it would be infeasible due to issues with heat dissipation. I suppose it could work if you had a very clever layout and employed rotation of some sort so that the problem areas don't overlap or if the clock speeds were intentionally kept low enough where nothing gets too hot, but that does potentially preclude it from some products.

Stack big cores on top of more low power utilitarian cores ?

 

[Joe NYC]

Stack big cores on top of more low power utilitarian cores ?

I wonder if a more fruitful approach would rather be just a fast interconnect at an intersect of dies.

Suppose there are 2 rectangular dies, and instead of stacking them on top of each other, the dies instead form an "L".

This way, nearly all of the surface area is eligible for contact with heatsink.

Looking at a package such as Milan, the area of the MCM is perhaps > 3x the area of the sum of the areas of the dies. So there is a plenty of space Even in Ryzen desktop chips.

In your example, the low power and high power don't have to be on top of each other for better performance (unlike, say L3). They just benefit from a fast link. So the small dies could be the horizontal part of the "L" and big cores the vertical part of the "L" and both would have heatsink on top of most of their area.

 

[DisEnchantment]

All of the biggliest details from the Gigabyte leak for Zen 4:

Details on the Gigabyte Leak

Recently, a ransomware group leaked data from Gigabyte in an attempt to extort payment. That’s been well covered by other outlets (please everyone, secure your networks), so here we’re …

chipsandcheese.com

GenZ and CXL in one go, awesome. SIs will be mighty pleased. NVDIMM-P seems supported as was in the original roadmap a long time ago.
The next gen servers from Intel and AMD would be transformative

Very sad that info has to come this instead of being willingly shared by AMD (like for example Intel Architecture day or previous Horizon events)

 

[DisEnchantment]

AMD Zen4 Ryzen CPUs confirmed to offer integrated graphics - VideoCardz.com

AMD to offer integrated on-chip graphics for next-gen Ryzen series The Next-generation of AMD Ryzen CPUs is now confirmed to offer integrated GPUs. Upcoming Ryzen CPU series based on Zen4 architecture will all offer integrated GPU by design. While this does not mean that literally all CPUs will...

videocardz.com

Seems the Zen4 APUs will support DP2.0, as per the block diagram for AM5 IO, which is not currently supported by RDNA2.
It could be a new update of DCN for RDNA2 iGPUs for which the support was planned to be added to Linux in this patch

[PATCH 0/6] Add DP 2.0 SST Support

 

[leoneazzurro]

There are solution being studied for cooling 3D stacked logic, i.e. by using a fluid inside the silicon stack.

 

[Mopetar]

There are solution being studied for cooling 3D stacked logic, i.e. by using a fluid inside the silicon stack.

That sounds interesting but difficult in reality since you need to use something that isn't going to expand too much at the sizes that are being used in top of a whole lot of other issues you'd run into at that level.

If you've got bottled anything it wants to expand as it heats up and that exerts more pressure on the container which needs to be strong enough to withstand that but also small enough to fit in a chip between the layers without ballooning the size too much or causing damage to the other layers.

 

[leoneazzurro]

That sounds interesting but difficult in reality since you need to use something that isn't going to expand too much at the sizes that are being used in top of a whole lot of other issues you'd run into at that level.

If you've got bottled anything it wants to expand as it heats up and that exerts more pressure on the container which needs to be strong enough to withstand that but also small enough to fit in a chip between the layers without ballooning the size too much or causing damage to the other layers.

Well this is why it is still at study and not already implemented (btw, if you keep the fluid flowing and without changing state there is no problem in the fluid itself, it is more a problem of the possible CTE mismatches between silicon and the materia used for containing the fluid).

 

[DisEnchantment]

12:49PM EDT - Zen4 by end of 2022

Hmm Seems Zen4 is going to take ~24 Months instead of the established 15 months cadence.
Either that or they are just being purposefully vague as shown in the slides. Otherwise a bit long considering Papermaster mentioned concurrent teams working on the designs.

 

[moinmoin]

12:49PM EDT - Zen4 by end of 2022

It's unclear from the live blog whether they actually said that or if that's just Ian's interpretation of the already known slide that ends at 2022. Either way AMD unfortunately really likes to be guarded these days even at these kind of events.