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

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Vattila

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Oct 22, 2004
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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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Dave3000

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Jan 10, 2011
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I don't think they are awkward, instead I feel like they provided the consumer with enough skus for you to make a choice based on the following scenarios.

Gaming only - 7800X3D
Productivity only - 7900X or 7950X
Mixed use - 7900X3D or 7950X3D

The only pushback seems to be about the core clocks being dialed back and lack of vcache on both CCDs. But where does a 7900X3D or 7950X3D with the same core clocks as the non X3D versions and double vcache really shine? What type of workloads? Seems like it would be very few use cases.

I guess you would have to buy the appropriate CPU for what you are going to do on your system, like you listed. For pure productivity and not gaming, I think the 7950X would be best out of all those you listed. For gaming I think the 7950X3D would offer the best flexibility including gaming flexibility, if you use a 3rd party program to manually assign which CCD the game will use and that's if the 3rd party program will support those CPU's. However, I'm not sure if it will be recommended to use a 3rd party scheduler such as Process Lasso for optimal application performance of the 7900X3D and 7950X3D or if Windows will be able to recognized what the application favors (v-cache/lower frequency or no v-cache/higher frequency) and assign the optimal CCD to the application accordingly. I wonder how consistent the the 7900X3D and 7950X3D will be in software that uses over 8 cores since each CCD has different performance characteristics on those CPU's. The reviews aren't out yet so I'm only presuming.
 
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Mopetar

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Jan 31, 2011
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AMD had a good thing going with Zen2 and Zen3. Why did they decide to screw up their huge power consumption advantage with Zen4?

After looking at the AT article on power scaling Zen 4 really falls off after 105W. My only guess is that they want to ensure greater headroom on AM5 for future products. Eventually we'll get more than 16C parts and not having the extra power would constrain those parts.

The board partners would be pretty upset if they're making boards that have to support TDPs for CPUs that aren't rated for them, so I'm guessing AMD decided to just push the chips beyond their efficiency point so board partners wouldn't complain.

What stops AMD from simply remapping vcache at the system level? Instead of throwing 32MB of L3 evenly across 16 cores, what stops them from adjusting it on the fly? If they wanted to throw 32MB at core0, and withhold the rest from core1--> core15, that could really mess with benchmarks. Likewise, a core having little benefit from L3 shouldn't hold any hostage from the others.

If it's a single core benchmark it will eventually get as much of the L3 cache as it can use since it's fully shared across all cores. There's not really a need (or a point) to dynamically adjust it like this. Never mind that doing this might require increasing the access time by a cycle or two to make sure the management policy is being followed.

Any core that's running a workload that fits inside its own L2 cache won't be evicting cache lines to the L3 very often, so it's not going to be taking up resources it doesn't really need.
 

Dave3000

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But does it benefit from more than 8 cores? If not, the 7800X3D is still the best option, no?

Based on the reviews I read, it doesn't seem so, at least for pure frame rate. However, I'm not sure if load times in this game benefit from more than 8 cores (CPU does play a role in load times). I think that 8 cores is enough for gaming for at least this console generation.
 

moinmoin

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I don't think they are awkward, instead I feel like they provided the consumer with enough skus for you to make a choice based on the following scenarios.
They are awkward in the sense that they offer a selling point for which to make use of no OS and software is prepared for yet.

Is it known for certain, or there's a reason why it can't be the other way around?
If it could be the other way around 7800X3D would boast a significantly higher max frequency.
 

PJVol

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May 25, 2020
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If it could be the other way around 7800X3D would boast a significantly higher max frequency.
Sorry, I don't see how 7800x3d boost frequency is relevant to the 2ccd chips L3 layout?
You're assuming the top CCD is 3D stacked, and I asked why it's not the lower binned CCD.
 
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moinmoin

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Sorry, I don't get, what 7800x3d has to do with the 2ccd l3 layout?
We have 7700X at max 5.4GHz whereas the CCDs with V-Cache all appear to max out at 5.0GHz. That's what 7800X3D maxs out at, if more were possible with V-Cache surely 7800X3D would have seen that. 7900X3D appears to add a 2nd CCD without V-Cache maxing out at 5.6GHz, and 7950X3D at 5.7GHz, both matching the max frequency of 7900X and 7950X respectively.
 

Timmah!

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Do you think that all core boost speed on the 3D cache models will be significantly slower than the regular versions?

This is the million dollar question. If the 7800 top boost is 400MHz lower than 7700 and is limited to 5GHz, will it clock to this value on all cores (like 7700x does i presume) or will it clock 300~400 MHz lower in that situation as well? Does 5800x3D clock lower in all core scenario compared to its limited single core boost?
 

moinmoin

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blckgrffn

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www.teamjuchems.com
I understand some gnashing of teeth here but the vcache is marketed for games and sits on a 8C/16T CCD. Not that many cache dependent games (that tend to lean on main thread or two) are going to escape from there.

With the full blown tiny core/big core approach from Intel for what a year plus now I fully expect schedulers to be able to figure this out. As others have pointed out, crowd the CPU the cache until its full is the most straight forward approach. The corner cases where you'd like the extra boost vs the cache are darn niche. I get that we are pedantic here but, again, this is for gaming first and foremost.

If I was buying a first gen 3D cache part on AM5 for gaming I wouldn't even consider the wider parts. No worries about anything, no paying for cores I would super rarely use. The actual frequency uplift from the 5800X3D seems really solid as well.

If you are using all the cores all the time, it'll be slightly more heterogenous, but still not quite as much as the current Intel approach.

What I want is benchmarks :)
 
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In2Photos

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They are awkward in the sense that they offer a selling point for which to make use of no OS and software is prepared for yet.
I seriously doubt that we are the first ones to realize that this may need some changes on the OS. Surely AMD realizes this which is why AMD said they have been working with Microsoft already.
I understand some gnashing of teeth here but the vcache is marketed for games and sits on a 8C/16T CCD. Not that many cache dependent games (that tend to lean on main thread or two) are going to escape from there.

With the full blown tiny core/big core approach from Intel for what a year plus now I fully expect schedulers to be able to figure this out. As others have pointed out, crowd the CPU the cache until its full is the most straight forward approach. The corner cases where you'd like the extra boost vs the cache are darn niche. I get that we are pedantic here but, again, this is for gaming first and foremost.

If I was buying a first gen 3D cache part on AM5 for gaming I wouldn't even consider the wider parts. No worries about anything, no paying for cores I would super rarely use. The actual frequency uplift from the 5800X3D seems really solid as well.

If you are using all the cores all the time, it'll be slightly more heterogenous, but still not quite as much as the current Intel approach.

What I want is benchmarks :)
Exactly!
 
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Kaluan

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I don't think they are awkward, instead I feel like they provided the consumer with enough skus for you to make a choice based on the following scenarios.

Gaming only - 7800X3D
Productivity only - 7900X or 7950X
Mixed use - 7900X3D or 7950X3D

The only pushback seems to be about the core clocks being dialed back and lack of vcache on both CCDs. But where does a 7900X3D or 7950X3D with the same core clocks as the non X3D versions and double vcache really shine? What type of workloads? Seems like it would be very few use cases.

Also may I just add, with all this negativity here, I don't think I've seen one(1) person comment (let alone positively) that we're getting 7000X3D in February, not the rumored March or later. That's a good thing? IDK I'm not sure anymore with all the gloom tinting. Everyone's too focused pointing and debating shortcomings, real or imagined or just minutiae.

Neither has there been much talk about expected pricing. I would be happy with $399 MSRP for the 7800X3D, slotting in above $349 quasi-MSRP 7700X and $329 MSRP (boxed w/ a cooler) 7700. But it's probably gonna be $449 or more.