AMD’s EPYC 7J13: Zen 3 Customized | Hacker News Reader

AMD’s EPYC 7J13: Zen 3 Customized

chipsandcheese.com

71 pointsrbanffy15 comments

I can't wait to see a similar review of Bergamo/Zen 4c. Die shot analysis shows the cores themselves, not counting the L3 cache, are also 35% smaller than regular cores. But most of the specs look the same. There's a huge mystery here and there have got to be some interesting sacrifices.

Maybe maybe maybe 4c is chiefly a process tweak, that going lower power let them use more aggressive process scaling. Maybe. But that's still a huge die-space reduction that makes me think there's some secrets like here in this chip, that chipsandcheese.com was able to uncover with read deep prying/benchmarking.

I do wish the graphs in this article had a comparison processor or two. A regular Zen 3 would be great.

As I recall, from the Zen 4c articles, the big concessions are slower L1/L2, which allows fewer transistors per byte and so smaller area; lower clock targets, which allows less buffering to make the clock domains work and so smaller area. The L3 is about the same as a Zen 4 chiplet, which means half the size per core. They also dropped support for v-cache, which saves a little bit of area too.

Prior to Zen4c, server and desktop chiplets were the same, and desktop chips need to clock to the moon for competitive reasons, but server chips aren't going to go to really high clocks anyway; the thermals are too challenging, so if there's enough demand to justify a separate spin for servers, it makes a lot of sense to tweak the design for reasonable clock rates that will be seen there.

I have had great success with the 'low-core / high-frequency' line-up in every step of the Zen+EPYC architectures.

They always have these (thanks to CCX and chiplets) SKUs and for latency-sensitive applications (or single-core non-parrallelized workloads), the high-frequency ones are amazing. You don't get the actual frequency/perf ratio, but they're relatively cheap (compared to the Intel SKUs with similar cores/freq) and damned reliable.

Frequency optimized parts were created to sidestep software licensing based on core count. Often w/ higher cache. Like Milan-X

https://www.semianalysis.com/p/zen-4c-amds-response-to-hyper...

I've been thinking about buying one of these, they show up on eBay as CPU+mobo+RAM combos as used cloud provider machines. Each CPU is 64C/128T, instead of the 15C exposed in the post's cloud VM. The rackmount cloud machines are dual CPU, for 128C/256T in 2u.

I'd prefer it in a tower case, but cooling (of not only the dual CPUs, but also the VRMs) is tricky.

Example: https://www.ebay.com/itm/195740808551 (a different 128C Epyc, for less than half the current cost of used same-gen Threadripper PRO with half the cores and no RAM..)

Comes down to power consumption at the end of the day. I worked out running a homelab was cheaper than cloud (for personal projects).

You're also better off with a newer consumer-level processor, the advancements made is that they use less power for much faster processes with less cores. The 7950x3d for example is great for databases.

> You're also better off with a newer consumer-level processor,

Strong disagree on this one. You can't even put 64GB of DDR5 into the latest consumer-level processors without causing bandwidth to halve down to DDR4 speeds (because of the two channel memory controller), and there's some talk of system instability even at the slow speeds. And you can't get more than 16 cores in the consumer-level CPU, vs. the 128 cores in the server machine I linked.

I’m doing this on b650d4u with success. 1.5k per machine or so but the clock speed is fantastic, good Remote Desktop performance as well. I can’t find reasonable cost server setups that can match this

Yep. And then investing in setting up a PIKVM has been the biggest gamechanger for me. You can grab a Pi4, then the rest of the parts from a reputable seller on aliexpress for a pretty decent price (HDMI thingy that plugs into the camera output on the pi, and OTG cables).

I just wish Pi's went back down to the normal price!

There are several variants of the 7713 like this. I have a couple of similar GCP cast-offs that have a 7B13 SKU.

Yeah not sure if there's a major difference.

Is it just to identify the cloud providers? 7J13 mentioned here is Oracle.

Mine don’t boost quite as high as a 7713, which might be a binning difference or a power saving measure. They were (relatively) cheap, so I have no complaints.

There is a list somewhere on STH of all the variant SKUs. The second letter does indeed indicate which cloud they were sold for.

Yes but not exactly. 7B13 was sold to both GCP and Alibaba. There are 2 variants of it with GCP having 60 cores and no turbo and Alibaba 64 and turbo. Looking at the part # won’t tell you which variant

They probably have one or more provider-specific networking bridges in them for zero-copy latched handling of packets into the machine's provider-specific SDN hardware (for accelerating SAN, IDS, etc.)

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