Thursday, January 5th 2023
AMD Confirms Ryzen 9 7950X3D and 7900X3D Feature 3DV Cache on Only One of the Two Chiplets
AMD today announced its new Ryzen 7000X3D high-end desktop processors to much fanfare, with availability slated for February 2023, you can read all about them in our older article. In our coverage, we noticed something odd about the cache sizes of the 12-core 7900X3D and 16-core 7950X3D. Whereas the 8-core, single-CCD 7800X3D comes with 104 MB of total cache (L2+L3), which works out to 1 MB L2 cache per core and 96 MB of L3 cache (32 MB on-die + 64 MB stacked 3DV cache); the dual-CCD 7900X3D and 7950X3D was shown with total caches of 140 MB and 144 MB, while they should have been 204 MB or 208 MB, respectively.
In our older article, we explored two possibilities—one that the 3DV cache is available on both CCDs but halved in size for whatever reason; and the second more outlandish possibility that only one of the two CCDs has stacked 3DV cache, while the other is a normal planar CCD with just the on-die 32 MB L3 cache. As it turns out, the latter theory is right! AMD put out high-resolution renders of the dual-CCD 7000X3D processors, where only one of the two CCDs is shown having the L3D (L3 cache die) stacked on top. Even real-world pictures of the older "Zen 3" 3DV cache CCDs from the 5800X3D or EPYC "Milan-X" processors show CCDs with 3DV caches having a distinct appearance with dividing lines between the L3D and the structural substrates over the regions of the CCD that have the CPU cores. In these renders, we see these lines drawn on only one of the two CCDs.
It shouldn't be hard for such an asymmetric cache setup to work in the real world from a software perspective, given that we are now firmly in the era of hybrid-core processors thanks to Intel and Arm. Even way before "Alder Lake," when AMD started shipping dual-CCD client processors with the Ryzen 3000 "Matisse" based on "Zen 2," the company closely collaborated with Microsoft to optimize OS scheduling such that high-performance and less-parallelized workloads such as games, are localized to just one of the two CCDs, to minimize DDR4 memory roundtrips.
Even before "Matisse," AMD and Microsoft confronted multi-threaded workload optimization challenges with dual-CCX architectures such as "Zen" and "Zen 2," where the OS scheduler would ideally want to localize gaming workload to a single CCX before saturating both CCXs on a single CCD, and then onward to the next CCD. This is achieved using methods such as CPPC2 preferred-core flagging, and which is why AMD highly recommends you to use their "Ryzen Balanced" Windows power-plan included with their Chipset drivers.
We predict that something similar is happening with the 12-core and 16-core 7000X3D processors—where gaming workloads can benefit from being localized to the 3DV cache-enabled CCD, and any spillover workloads (such as audio stack, network stack, background services, etc) are handled by the second CCD. In non-gaming workloads that scale across all 16 cores, the processor works like any other multi-core chip, it's just that the cores in the 3DV-enabled CCD have better performance from the larger victim cache. There shouldn't be any runtime errors arising from ISA mismatch, as the CPU core types on both CCDs are the same "Zen 4."
AMD Ryzen 7000X3D processors go on sale in February 2023.
In our older article, we explored two possibilities—one that the 3DV cache is available on both CCDs but halved in size for whatever reason; and the second more outlandish possibility that only one of the two CCDs has stacked 3DV cache, while the other is a normal planar CCD with just the on-die 32 MB L3 cache. As it turns out, the latter theory is right! AMD put out high-resolution renders of the dual-CCD 7000X3D processors, where only one of the two CCDs is shown having the L3D (L3 cache die) stacked on top. Even real-world pictures of the older "Zen 3" 3DV cache CCDs from the 5800X3D or EPYC "Milan-X" processors show CCDs with 3DV caches having a distinct appearance with dividing lines between the L3D and the structural substrates over the regions of the CCD that have the CPU cores. In these renders, we see these lines drawn on only one of the two CCDs.
Even before "Matisse," AMD and Microsoft confronted multi-threaded workload optimization challenges with dual-CCX architectures such as "Zen" and "Zen 2," where the OS scheduler would ideally want to localize gaming workload to a single CCX before saturating both CCXs on a single CCD, and then onward to the next CCD. This is achieved using methods such as CPPC2 preferred-core flagging, and which is why AMD highly recommends you to use their "Ryzen Balanced" Windows power-plan included with their Chipset drivers.
We predict that something similar is happening with the 12-core and 16-core 7000X3D processors—where gaming workloads can benefit from being localized to the 3DV cache-enabled CCD, and any spillover workloads (such as audio stack, network stack, background services, etc) are handled by the second CCD. In non-gaming workloads that scale across all 16 cores, the processor works like any other multi-core chip, it's just that the cores in the 3DV-enabled CCD have better performance from the larger victim cache. There shouldn't be any runtime errors arising from ISA mismatch, as the CPU core types on both CCDs are the same "Zen 4."
AMD Ryzen 7000X3D processors go on sale in February 2023.
164 Comments on AMD Confirms Ryzen 9 7950X3D and 7900X3D Feature 3DV Cache on Only One of the Two Chiplets
The reason the cache is on 1 ccd is also to avoid the latency penalty of 2 ccd's.
Adding that on the other ccd will just cause both to have lower clocks instead of just 1 and will reintroduce that latency penalty.
With the Windows 11 tweaks games will choose the ccd with cache on it over the other.The reason for this is the 7800X3D is a single CCD design with V-cache so clocks are lower.
The 7900 and 7950X3D chips only have v-cache on 1 ccd. The reason you are not seeing reduce clocks is because that is from the ccd without cache.
While the 7900X3D and 7950X3D have only 1 CCD with 3D Cache the other CCD will run at the faster speed. You can expect the 3D Cache CCD to also be limited to 4.0-4.2GHz instead of the higher base clock given. This is also why the 5800X3D was slower and why the 7800X3D has a lower base and boost clock than the other 2. The 3D Cache will likely have problems going faster than that so that CCD will run slower.
However we will see benchmarks in 6 weeks or so. However I don't see the need at this time for more than 8 cores for gaming. even seeing 6 cores used is still rare. As far as I know only Cyberpunk 2077 profits from having 8 cores. The rest is max 6 before the FPS stays the same.
Spiderman Remastered/ Miles Morales with RT on is very cpu heavy.
And there will be more coming this year.
The trolling on this forum is getting out of hand anymore.
Perhaps because 7800x3d is 5GHz, they used naming to cover up its low clock speed.I wish they could sell naked GPUs (only PCB)
bcz for a non-gaming applications; 7700x is faster and cheaper, so why 7800x3d comes with embedded graphics?
I personally believe that all CPUs should come with an iGPU, at least for troubleshooting purposes.
Does anyone know if AMD used a 4090 or 7900 xtx for those first party charts?
It seems not only pricing but scheduling will make or break R9 Zen4 3d cpus.
Just for reference the 5800x3d went from $449 to $329 from January 2022 to November 2022 ( $400 in October). The potential customer base for 5800x3d was multiple generations of AM4 customers. Ryzen 4 3d chips might seemed very hyped initially but the demand should be significantly less than 5800x3d. Plus we now have 3 cpus to choose from. Hence why AMD didn't finalize prices yet.
Final thoughts wait for multiple 3d party benchmarks before purchasing decision these will likely have enough stock just based on the higher AM5 cost for new customers to swallow compared to 5800x3d drop in existing am4 mobo user base.
Even with the limited boost on the 7800X3D and 5800X3D, they have world class performance for gaming. Now, you literally can have your cake and eat it too.
Thread management will be an issue if Windows thinks that the highest boosting cores are the best.