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

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Vattila

Vattila

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Except for the details about the improvements in the microarchitecture, we now know pretty well what to expect with Zen 3.

The leaked presentation by AMD Senior Manager Martin Hilgeman shows that EPYC 3 "Milan" will, as promised and expected, reuse the current platform (SP3), and the system architecture and packaging looks to be the same, with the same 9-die chiplet design and the same maximum core and thread-count (no SMT-4, contrary to rumour). The biggest change revealed so far is the enlargement of the compute complex from 4 cores to 8 cores, all sharing a larger L3 cache ("32+ MB", likely to double to 64 MB, I think).

Hilgeman's slides did also show that EPYC 4 "Genoa" is in the definition phase (or was at the time of the presentation in September, at least), and will come with a new platform (SP5), with new memory support (likely DDR5).

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What else do you think we will see with Zen 4? PCI-Express 5 support? Increased core-count? 4-way SMT? New packaging (interposer, 2.5D, 3D)? Integrated memory on package (HBM)?

Vote in the poll and share your thoughts! :)
 
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CakeMonster

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Hard to guess or plan for the arrival of the 3D/cache models though, will they be as late as the Zen3 one? Might as well get regular Z4 if you need an upgrade now, especially if you can't count on them making other models than 7800X3D.
 
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yuri69

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nicalandia said:
Zen5 is not a "Refresh" from Zen4, Zen4 it's a Refresh or midway upgrade from Zen3.

The entire Zen4 stack is design to compete favorably against ADL/RPL and MTL. Zen4 is enough to put a hurting on Alder Lake, Zen4 3D V-Cache will keep/regain any gaming crown and Zen4c exceed at throughput..
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Sorry, bad wording on my side (it's pretty late). Zen 4 is the "refresh", not Zen 5.
 
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inf64

inf64

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Now that we have the official slide from AMD, ~10% ST IPC is a disappointment given the new node and opportunities it presented. It's basically their lowest IPC effort in 5 years (since original Zen). Maybe they thought this would be enough, coupled with clock and perf./watt improvements, who knows. It seems they did focus on Zen5 more, but if Zen5 brings ~19% gain versus Zen4 then it might not be enough to fight off next gen intel cores. AMD has definitely slowed down, let's hope Zen5 is a big hitter.

On the other hand, my Zen4 performance projection looks to be spot on, yet again :D. I missed the IPC by 3%, and it looks like the clock speeds will be roughly in the ballpark. Zen4 will be very competitive with Raptor lake, having almost exactly the same IPC as Alder Lake and higher clocks (like Raptor Lake). It will all come down to whether Raptor lake P cores have any IPC improvements or they are more like IceLake->TigerLake evolution. I would never touch a hybrid design myself, especially if I had a choice to pick 16 top performance P cores on a smaller node versus the hybrid chip such as Raptor Lake.
 
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CakeMonster

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inf64 said:
I would never touch a hybrid design myself, especially if I had a choice to pick 16 top performance P cores on a smaller node versus the hybrid chip such as Raptor Lake.
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I'm all for hybrid or b.L in the long run, it makes sense with ST demands for gaming while having tons of small cores for MT loads. I'm really looking forward to that future.

However, as for upgrading this fall, Z4 is definitely the most tempting prospect, not having to deal with thread scheduling or W11. Unless RL is ahead by several % I will go with AMD. I really hope there's no shortage this time, because those who didn't order Z3 on release day had to wait a _long_ time for it to arrive. Ideally I want to know how both Z4 and RL performs, but if RL will be out much later, I might have to gamble on Z4.
 
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yuri69

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inf64 said:
AMD has definitely slowed down, let's hope Zen5 is a big hitter.
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This is kinda strange given the main idea was the multi-generational Zen success had been enabling cash flow for R&D. But apparently, that was not the case.

Looking at Zen 5 slide again it seems a bit concerning. They got three bullet points for their initial reveal:

* "Enhanced performance and efficiency" - Next-gens are naturally faster and more efficient. Zen 5 has a node advantage and comes <2 years after Zen 4.
* "Re-pipelined front end and wide issue" - This one is great - the 5th gen finally goes wider.
* "Integrated AI/ML optimizations" - Ugh, ISA extensions. OK, every gen brings some.

Two of three do not really bring any important info. This is strange.
 
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Ajay

Ajay

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nicalandia said:
Zen5 is not a "Refresh" from Zen4, Zen4 it's a Refresh or midway upgrade from Zen3.

The entire Zen4 stack is design to compete favorably against ADL/RPL and MTL. Zen4 is enough to put a hurting on Alder Lake, Zen4 3D V-Cache will keep/regain any gaming crown and Zen4c exceed at throughput..
Click to expand...

The Zen4 design stack is first designed for EPYC systems, to compete with Intel on the server side. Then any accommodations for laptop/desktop needed come second (and mainly in the form of Zen4 CPUs that don't make the cut in terms of efficiency for the desktop CPUs that we use). Server first clearly took over in Zen2. Zen1 was designed more to get AMD's foot in the door, mainly in the desktop market.
 
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gdansk

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yuri69 said:
This is kinda strange given the main idea was the multi-generational Zen success had been enabling cash flow for R&D. But apparently, that was not the case.

Looking at Zen 5 slide again it seems a bit concerning. They got three bullet points for their initial reveal:

* "Enhanced performance and efficiency" - Next-gens are naturally faster and more efficient. Zen 5 has a node advantage and comes <2 years after Zen 4.
* "Re-pipelined front end and wide issue" - This one is great - the 5th gen finally goes wider.
* "Integrated AI/ML optimizations" - Ugh, ISA extensions. OK, every gen brings some.

Two of three do not really bring any important info. This is strange.
Click to expand...
But wider is very important information. They are currently competing against wider designs effectively. If widened properly it could be a big improvement.
 
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inf64

inf64

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yuri69 said:
This is kinda strange given the main idea was the multi-generational Zen success had been enabling cash flow for R&D. But apparently, that was not the case.

Looking at Zen 5 slide again it seems a bit concerning. They got three bullet points for their initial reveal:

* "Enhanced performance and efficiency" - Next-gens are naturally faster and more efficient. Zen 5 has a node advantage and comes <2 years after Zen 4.
* "Re-pipelined front end and wide issue" - This one is great - the 5th gen finally goes wider.
* "Integrated AI/ML optimizations" - Ugh, ISA extensions. OK, every gen brings some.

Two of three do not really bring any important info. This is strange.
Click to expand...
It's the extend of the changes Zen5 brings. We know each new generation brings some improvements, and for AMD it was the odd number in the Zen generation roadmap: Zen1->Zen3->Zen5.

AMD has stated in the past that they targeted 40% gen-on-gen IPC jumps. This has been true for Excavator->Zen1 as they targeted 40%, and achieved 52%. Zen1-> Zen3 brought us 1.03(Zen1+) x 1.15(Zen2) x 1.19 (Zen3) ~= 1.41 or ~40% IPC jump, just as they planned. For Zen5 to achieve the same, it would need to have a massive 1.4 (Zen5 target)/ 1.1 (Zen4) = 1.27 or 27% IPC increase Vs vanilla Zen4 cores. It's not impossible, but it's hard to expect they will manage to gain so much even with a much wider core. Zen4 does look like a missed opportunity on the IPC front.
 
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exquisitechar

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Overall, my impression of Zen 4 is the same as after Computex. Underwhelming, but the power curve will really make or break it in my eyes. Raphael will not be great, seemingly matching or slightly surpassing ADL in ST performance at best, with a node advantage, one year later. Of course, Raphael is mostly an afterthought for AMD. With Intel's incompetence and constant delays in the server market especially, such as the latest SPR delay, the future is looking very bright for Genoa. Really interested in how Phoenix performs as well, hence the aforementioned power curve.

Zen 5 really needs to deliver.
uzzi38 said:
Are you claiming there's going to be a Zen 4 refresh in late 2024?

Are you trying to look like a clown?
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I believe he meant that there would be something like Zen+ a year or so after Zen 4 and that there would be about two full years between Zen 4 and Zen 5.
 
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gdansk

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Markfw said:
Nobody linked this pic. >35% overall performance improvement. Thats more like it ! Well, cinebench at least. And performance per watt does not suggest ADL like power consumption.

View attachment 62849
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In fact that's what people have been expecting for MT all along due to the higher TDP. You have to remember it's two different charts too. It may be 25% more performance per watt but that >35% is when not at the same power level. They're throwing another ~90W at it to get that last >10%. And unfortunately that will be putting its power consumption much closer to ADL than the 5950X was, out of the box. Of course it is promising for people who set their own PPT.
 
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moinmoin

moinmoin

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Ajay said:
Server first clearly took over in Zen2. Zen1 was designed more to get AMD's foot in the door, mainly in the desktop market.
Click to expand...
Zen has been server first from the very beginning. The very first Zen design, the Zeppelin die, was designed to work in a group of four, for servers. The consumer oriented designs are the mobile APUs. Arguably the first actual desktop specific design is Raphael's IOD including a minimalist iGPU, though that may or may not be part of mobile Dragon Range as well.
 
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nicalandia

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inf64 said:
Now that we have the official slide from AMD, ~10% ST IPC is a disappointment given the new node and opportunities it presented. It's basically their lowest IPC effort in 5 years (since original Zen).
Click to expand...
Why so disappointed?

Zen3 over Zen2 saw a 12% performance boost in application performance and 22% on gaming. AMD has yet to release gaming performance on Zen4 but due to the large L2$ you can bet that it's >15%
 
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inf64

inf64

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nicalandia said:
Why so disappointed?

Zen3 over Zen2 saw a 12% performance boost in application performance and 22% on gaming. AMD has yet to release gaming performance on Zen4 but due to the large L2$ you can bet that it's >15%
Click to expand...
Zen3 did bring 12% IPC performance versus Zen2 but only in MT apps. In ST apps, the IPC was as AMD claimed ~19%. This was partly due to halved/core L3 bandwidth versus Zen2, as this was mostly noticed in heavy MT workloads that taxed the L3 a lot.

There is some hope that MT IPC on Zen4 could be even higher than 10% *if* AMD "fixed" the L3 cache BW/core and doubled it. Doubled L2 should also help a lot in workloads such as games, but the effect of it should be in single digits (looking at the overall ~10% IPC claim).

Zen4 is a disappointment in IPC terms as AMD spoiled us with fantastic gains in the past (>15% basically). They do make up for it with AVX512 and much higher effective clocks, so overall the performance jump from Zen3->Zen4 could very well be greater than what we had from Zen2->Zen3.

Racan said:
Gaming wise I think we'll have to wait for 3d cache Zen 4 to tie or beat Raptor Lake.
Click to expand...
Raptor Lake first needs to beat a lowly 8C Zen3D in games ;)
 
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gdansk

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Racan said:
Gaming wise I think we'll have to wait for 3d cache Zen 4 to tie or beat Raptor Lake.
Click to expand...
We'll see, games love clock rates too and it appears they'll end up pretty close. First time AMD and Intel will be close in both clock rate and IPC for years... it will be interesting.
 
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Det0x

Det0x

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Some napkin math from me :)

So if we assume that Cinebench is among the worst case (low end of the scale) in terms of "IPC" increase from Zen3 to Zen4, ref this picture: (Cinebench r20 ST is + 13% while geomean is 19%)
1654812649707.png

Zen3 fmax 5050mhz VS Zen4 fmax 5850mhz = ~15% higher peak clockspeeds (sustain clocks probably see an even bigger increase)

ST Performance base (Zen3) x 1.10 IPC x increased clock speed by 15% = ~26% higher ST performance in "worst case apps" like Cinebnench R23

In games, we can probably/maybe quickly get "+20% IPC" or more considering doubling the L2 cache that Cinebench does not care about.

Gaming performance (Zen3) x 1.2 IPC x increased clock speed by 15% = ~38% higher performance in "games". (or more thanks to better sustained clocks)

On top of this we get the benefit from going from DDR4 to DDR5 with hopefully much higher infinity fabric clockspeeds, which has limited Zen3 performance in games (latency) from the get-go.

All in all, not bad i would say ;)
 
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