On Friday, AMD launched its latest monster CPU—the 64-core, 128-thread Threadripper 3990x. The 3990x isn't the first publicly available 128-threaded x86-64 CPU—that honor goes to AMD's Epyc 7742, 7702, and 7702P in a three-way tie. But the 3990X is the first "desktop" CPU offering that many threads—and it's stretching the ecosystem in doing so.
Cost per thread
Despite the groundbreaking specs on the TR3990x, AMD is adhering to the same pricing strategy it has employed for years now—pick the CPU that fits your needs and pay a reasonable, roughly linearly scaled price for it. If you want Threadripper CPU threads, you're going to pay roughly $30 apiece for them, whether you're looking for the smaller or larger parts.
| Processor | Cores/Threads | Cost | Cost per thread |
| AMD Threadripper 3990x | 64/128 | $3,990 | $31.17 |
| AMD Threadripper 3970x | 32/64 | $1,999 | $31.23 |
| AMD Threadripper 3960x | 24/48 | $1,399 | $29.15 |
| AMD Epyc 7702P | 64/128 | $4,784 | $37.36 |
| Intel Xeon Platinum 9282 | 56/112 | $30,000 (?) | $267.86 (?) |
| Intel Core i9-10980XE | 18/36 | $1,000 | $27.78 |
| Intel Core i9-9980XE | 18/36 | $1,979 | $54.97 |
This is in sharp contrast to Intel's pricing strategies, which have tended for years to run more toward "pick the CPU you can afford" than "pick the CPU that fits your needs." The best example of this strategy is Intel's top-of-the-line Intel Xeon Platinum series, which literally cannot be priced—they're not available in retail—but can be reasonably estimated to cost roughly ten times as much per thread as the closest competing Epyc parts.
However, we can see a big change in Intel's HEDT (High End DeskTop) CPU pricing strategy since 3rd-generation Threadripper launched. Team Blue slashed the price for its flagship HEDT part in half in a single year. This brought the top Core i9 part's cost per thread in line with—and even a little cheaper than—the competing Threadripper parts.
Moving back to Team Red, the 64-core Threadripper is a bit cheaper than the 64-core, single-socket Epyc 7702P—but not enough to write home about. This leaves the decision between building a system around TR3990x or 7702P, again, more focused on finding a build that suits the workflow instead of a cost that fits your wallet.
Why (or why not) Threadripper?
Threadripper and Epyc have more in common than not. Both families offer incredible core counts, support for ECC RAM, and relatively high numbers of PCIe 4.0 lanes—and with the cost per thread in shouting distance of one another, that means a careful system builder can worry about the remaining differences between the architectures rather than overall cost.
3rd-generation Threadripper can usefully be thought of as a 3rd-generation Epyc with higher clock speeds but fewer PCIe 4.0 lanes, fewer memory channels, and support for less total RAM. It's an optimal setup for jobs like 3D rendering that typically bottleneck on raw, massively multi-threaded CPU performance—but not so much for jobs bottlenecking on memory throughput or requiring massive in-memory datasets.
As reported in Anandtech's excellent Threadripper 3990x review, the newest Threadripper is also pushing the boundaries of what the industry is prepared to consider a "desktop" in the first place. Windows 10 Professional chokes pretty badly when presented with TR3990x's 128 logical processors (threads) and organizes them as two CPU groups—which it even mistakenly refers to as multiple "sockets" in some places.
Windows 10 Pro's lack of support for so many threads on a single socket isn't just a funny-looking quirk. Under Windows 10 Pro, some benchmarks run twice as fast with hyperthreading disabled, just to keep the operating system from maladaptively grouping them into separate "sockets" that then get handled under NUMA rules. Keeping threads from crossing real physical processor boundaries is helpful, but it can be crippling when the actual boundary doesn't exist in the first place.
Ultimately, this means Windows 10 Pro isn't really appropriate for Threadripper 3990x at all—if you're building a 3990x system, you need to plan on a roughly $120 upgrade from Pro to Workstation or on paying the $84/year for a Windows 10 Enterprise subscription. Windows 10 Workstation and Enterprise both support TR3990x's 128 threads without resorting to organizing them in nonexistent sockets, and without the performance penalties associated.
None of this is a problem for Linux users. Although Intel's performance-optimized Clear Linux distribution outperforms normal "daily driver" distributions, it doesn't do so any more on the Threadripper 3990x than it does on a lowly quad-core Ryzen 5 3400G. If you want to run a 3900x on bone-stock Ubuntu, you can do so, and you'll be fine.
Conclusions
Threadripper 3990x, like the 3970x that came before it, is a very specialized beast. If you need the massive number of threads either CPU brings to bear and don't need more than 256GB RAM, they're kind of a no-brainer. But it's a mistake to think of them as optimal CPUs for gaming, or for any workload that doesn't make effective use of their massive parallelism. While they're no slower for single-threaded or lightly multithreaded tasks than the much less expensive Ryzen 9 3950X, they're not any faster at those tasks, either—and they're considerably less efficient.
The good
- 128 threads—oh my! Nobody's ever made a 128-thread HEDT CPU before.
- Cost per thread isn't significantly higher than other Threadripper (or competing Intel) HEDT parts.
- Already available in retail OEM systems—including OEM Linux workstations.
- Compiles a modern Linux kernel in 24 seconds.
The bad
- No AVX-512 / Deep Learning Boost x86 instructions—AVX-512 workloads will run faster on much smaller, cheaper Intel CPUs.
- 128 threads—oh my! Some operating systems and applications can't really cope with this scale yet.
- Even maxed out with the newest RAM, 256GB/128 threads only comes out to an average of 2GB RAM per CPU thread.
The ugly
- Sharing office space with a Threadripper system in a South Carolina summer.
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