AMD Zen 2 Microarchitecture Analysis: Ryzen 3000 and EPYC Rome
by Dr. Ian Cutress on June 10, 2019 7:22 PM EST- Posted in
- CPUs
- AMD
- Ryzen
- EPYC
- Infinity Fabric
- PCIe 4.0
- Zen 2
- Rome
- Ryzen 3000
- Ryzen 3rd Gen
Building a core like Zen 2 requires more than just building a core. The interplay between the core, the SoC design, and then the platform requires different internal teams to come together to create a level of synergy that working separately lacks. What AMD has done with the chiplet design and Zen 2 shows great promise, not only in taking advantage of smaller process nodes, but also driving one path on the future of compute.
When going down a process node, the main advantages are lower power. That can be taken in a few ways: lower power for operation at the same performance, or more power budget to do more. We see this with core designs over time: as more power budget is opened or different units within the core get more efficient, that extra power is used to drive cores wider, hopefully increasing raw instruction rate. It’s not an easy equation to solve, as there are many trade-offs: one such example in the Zen 2 core is the relationship between the reduced L1 I-cache that has allowed AMD to double the micro-op cache, which overall AMD expects to help with performance and power. Going into the minutae of what might be possible, at least at a high level, is like playing with Lego for these engineers.
All that being said, Zen 2 looks a lot like Zen. It is part of the same family, which means it looks very similar. What AMD has done with the platform, enabling PCIe 4.0, and putting the design in place to rid the server processors of the NUMA-like environment is going to help AMD in the long run. The outlook is good for AMD here, depending on how high it can drive the frequency of the server parts, but Zen 2 plus Rome is going to remove a good number of questions that customers on the fence had about Zen.
Overall AMD has quoted a +15% core performance improvement with Zen 2 over Zen+. With the core changes, at a high level, that certainly looks feasible. Users focused on performance will love the new 16-core Ryzen 9 3950X, while the processor seems nice an efficient at 105W, so it will be interesting so see what happens at lower power. We're also anticipating a very strong Rome launch here over the next few months, especially with features like double FP performance and QoS, and the raw multithreading performance of 64 cores is going to be an interesting disruptor to the market, especially if priced effectively. We’ll be getting the hardware on hand here soon to present our findings when the processors are launched on July 7th.
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wurizen - Friday, June 14, 2019 - link
flex^^^wurizen - Friday, June 14, 2019 - link
OMFG! I. Am. Not. Talking. About. Intel. Mesh.I. Am. Talking. About. Infinity. Fabric. High. Memory. Latency!
Now that I got that off my chest, let's proceed shall we...
OMFG!
L3 Cache? WTF!
Do you think you're so clever to talk about L3 cache to show off your knowledge as if to convince ppl here you know something? Nah, man!
WTF are you talking about L3 cache, dude? Come on, dude, get with the program.
The program is "Cross-CCX-High-Memory-Latency" with Infinity Fabric 1.0
And, games (BO3, BF1, BF4 from my testing) are what is affected by this high latency penalty in real-time. Imagine playing a game of BO3 while throughout the game, the game is "micro-pausing" "Micro-slow-motioning" repeatedly throughout the match? Yep, you got it, it makes it unplayeable.
In productive work like video editing, I would not see the high latency as an issue unless it affects "timeline editing" causing it to lag, as well.
I have heard some complain issues with it in audio editing with audio work. But I don't do that so I can't say.
As for "compute-intensive applications (y'know, real work)" --delatFx2
....
.....
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You duh man, bruh! a real compute-intensive, man!
"This article mentions a Windows 10 patch to ensure that threads get assigned to the same CCX before going to the adjacent one." --deltaFx2
Uhhh... that won't fix it. Only AMD can fix it in Infinity Fabric 2.0 (Ryzen 2), if, indeed, AMD has fixed it. By making it faster! And/or, reducing that ~110ns latency to around 69ns.
Now, my question is, and you (deltaFx2) hasn't mentioned it in your wise-response to my comments is that SLIDE of "Raw Memory Performance" showing 69ns latency at 3200 Mhz RAM. Is that Raw memory performance Intra-CCX-Memory-Performance or Inter-core-Memory-Performance? Bada-boom, bish!
wurizen - Friday, June 14, 2019 - link
it's a problem ppl are having, if you search enough....Alistair - Wednesday, June 12, 2019 - link
those kinds of micro stutters are usually motherboard or most likely your windows installation causing it, reinstall windows, then try a different motherboard maybewurizen - Wednesday, June 12, 2019 - link
Wow, really? Re-install windows?I just wanna know (cough, cough Anand) what the Cross-CCX-Latency is for Ryzen 2 and Infinity Fabric 2.0.
If, it is still ~110ns like before.... well, guess what? 110 nano-effin-seconds is not fast enough. It's too HIGH a latency!
You can't update bios/motherboard or re-install windows, or get 6000 Mhz RAM (the price for that, tjo?) to fix it. (As shown in the graph for whatever "Raw Memory Latency" is for that 3200 Mhz RAM to 3600 Mhz stays at 69 ns and only at 37333 Mhz RAM does it drop to 67ns?).... This is the same result PCPER did with Ryzen IF 1.0 showing that getting Faster RAM at 3200 Mhz did not improve the Cross-CCX-Memory-Latency....
supdawgwtfd - Thursday, June 13, 2019 - link
O don't get any stutters with my 1600.As above. It's nothing to do with the CPU directly.
Something else is causing the problem.
deltaFx2 - Thursday, June 13, 2019 - link
How so you know for sure that the microstutter or whatever it is you think you are facing is due to the inter-ccx latency? Did you actually pin threads to CCXs to confirm this theory? Do you know when inter-ccx latency even comes into play? Inter-ccx latency ONLY matters for shared memory being modified by different threads; this should be a tiny fraction of your execution time, otherwise you are not much better going multithreaded. Moreover, Each CCX runs 8 threads so are you saying your game uses more than 8? That would be an interesting game indeed, given that intel's mainstream gaming CPUs don't have a problem on 4c8t.To me, you've just jumped the the gun and gone from "I have got some microstutter issues" to "I know PCPer ran some microbenchmark to find out the latency" to "that must be the problem". It does not follow.
FreckledTrout - Thursday, June 13, 2019 - link
I agree. If micro stutter from CCX latency was really occurring this would be a huge issue. These issues really have to be something unrelated.wurizen - Friday, June 14, 2019 - link
Another thing that was weird was GPU usage drop from 98% to like 0% in-game, midst-action, while I was playing... constantly, in a repeated pattern throughout the game... this is not a server or games hitching. we understand as gamers that a game will "hitch" once in a while. this is like "slow-motion" "micro-pause" thing happening through out the game. happens in single player (BF1) so I ruled out server-side. It's like the game goes in "slow-motion" for a second... not once or twice in a match, per se. But, throughout and in a repeated constant fashion... along with seeing GPU usage to accompany the effect dropping from 98% or so (normal) to 0% for split seconds (again, not once or twice in a match; but a constant, repeated pattern throughout the match)And, there are people having head-scratching issues similar to me with Ryzen CPU.
No one (cough, cough Anand; nor youtube tech tubers will address it) seems to address it tho.
But, I think that Ryzen 2 is coming out and if Cross-CCX-High-LAtency-Issue is the same, then we're bound to hear more. I'm sure.
I am thinking tech sites are giving AMD a chance... but not sure... doesn't matter tho. I got a 7700k (I wanted the 8-core thing when 1700x Ryzen came out) but its fine. Im not a fanboy. Just a techboy.... if anything...
wurizen - Friday, June 14, 2019 - link
The "micro-stutter" or "micro-pausing" is not once or twice (I get those with Intel, as well) but, a repeated, constant pattern throughout the match and round of game. The "micro-stutter" and "micro-pause" also "FEELS" different than what I felt with my prior 3700K CPU and current 7700K CPU. It's like a "micro-slow-motion." I am not making this up. I am not crazy!