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Hyperthreading doesn't even get close to doubling actual performance, it depends on the workload but AMDs Zen5 gains about 15% from HT on average according to Phoronix's benchmarks.

https://www.phoronix.com/review/amd-ryzen-zen5-smt/8

In practice on Zen1 and Zen3 I found HT to provide 20% to 25%.

It seems some benchmarks are as high as 50% with zen5.

AMD really improved HT with Zen 5 by adding a second instruction decoder per core. I expect even better per-thread performance from Zen 6.

There's also the added fun that using hyperthreading/SMT cores impacts your workload on the corresponding primary cores as well. Depending on your workload SMT can end up being a throughput/latency trade off you might not have been aware of.

Ampere doesn't do SMT, so you get comparable performance across the board.

I mentioned it a couple times in the article, but here's a bullet point right in the conclusion:

> "Arm is more efficient": that's not always true—AMD just built the most efficient 192 core server this year, beating Ampere

I also talk about idle power draw being very high in comparison to AMD.

Since I don't have a Turin system to test I didn't do direct wattage comparisons but recommended the linked Phoronix comparison.

Jeff says as much. The AMD EPYC core does offer better performance per watt, which says more about AMD than it does about Ampere.

But also this: "The big difference is the AmpereOne A192-32X is $5,555, while the EPYC 9965 is almost $15,000!"

So you have to look at TCO over a period of years, but that's still quite significant.

Dad of a friend ran a store selling designer underwear for men. He sold boxer shorts for $70 over 25 years ago.

He once told me that he also had a rack of thongs. Now, the thongs didn't have a lot of material, obviously, and were inexpensive to manufacture, so if he'd do his regular markup on them they'd end up selling for $15.

"However, notice the price tag is $25. I add an extra $10, because if a guy's looking to buy a thong, he's going to buy a thong".

I think about what he said when I see the chip prices on these high-end server CPUs.

Wondering who actually pays public price on those AMD chips in big-OEM servers. Not saying the AmpereOne isn't also discount-able too, but these public prices always feel like signalling, to me, more than a reference to the actual price. Or maybe I'm lucky...

The 9965 is a much faster chip than the Ampere, but also it is at the point of diminishing returns. The Ampere struggles to match much cheaper AMD offerings in the phoronix suite, it is not better value at all.

> $5k vs $15k

> So you have to look at TCO over a period of years, but that's still quite significant.

Your point is a valid point. However if we're talking TCO, we should also factor in that TCO also does involve rack space, power (and power efficiency), cooling, cabling, ports on the ToR switch, so on and so forth.

The AMD solution halves pretty much everything around the CPU, and in order to get the same thread count you should really compare 2x$5k vs $15k.

I get that SMT does have performance hits, but such performance penalties mostly show up when you're doing number crunching all day every day. In real world scenarios, where software spends a lot of time waiting either for disk i/o or for network i/o I would expect that to be a non-issue.

AMD's offering is still competitive, in my opinion.

In the video Jeff mentions that the EPYC CPU wins in performance per watt but not per dollar because it's 3x the cost.

$15,000 CPU is better than a $5000 CPU?

You can do all the benchmarks you want, but if you don't factor in price, then of course the more expensive product (in general) is going to be better.

It is the same thing with the Snapdragon Elite and Mediatek Dimensity 9400. The SDE is the faster processor and more expensive.

> but has hyper-threading (!!!) meaning you get 384 threads... So this means that AMD is essentially on par with ARM cpus

So you’re saying ‘essentially’ an AMD thread is the same as an ampere core?!

Always has been. Most ARM cores are closer to x86 E-cores.

Ampere cores are not ‘most Arm cores’

Last time I looked at Ampere it was way less power hub but then the competition. EPYC is over 250W at idle!

Off the top of my head, the Ampere 128 core was 250W at max load. Big difference.

Only issue I had was cache size, and you could only buy them from NewEgg.

Oh… and the dual socket gigabyte board had the sockets too close together that I’d you put a big ass heat sink and fan, the outlet of one fan will go straight into the inlet of the other!

I think you might be comparing your memories of Ampere's CPU power draw to either a full Epyc server's wall power draw or stated TDP. The 128 core EPYC 9754 in the chart linked above has a min of 10 W and a max draw of 397 W even though it outperforms the new 192 core variant AmpereOne A192-32X which had a min of 102 W and a max of 401 W.

The min on the A192 does seem anonymously high though. That said, even the M128-30 has a min of 21 W or about twice that of the AmpereOne.

Hmmm. Weird because I was definitely out odd EPYC because of idle draw. Ok thanks, that’s back on the table now!!

I wasn't been able to get my 2nd gen EPYC 7642 idle under 100W. Most of that power goes to the I/O die. The cores themselves manage their power very well. While I have all memory slots as well as a number of PCIe lanes occupied (more than 24 available from the consumer chips, but probably less than 48...,) I routinely think about side-grading to something else just to reduce the idle power consumption.

I would be hard pressed to believe that another EPYC would be able to significantly reduce I/O die power consumption significantly, given that AMD hasn't really made many major changes to it over the generations.

Thanks, and damn I guess…

Maybe I should wait another 18 month cycle

Sorry… another question - what would you recommend these days for a home machine in an office (i.e not a loud and hot rack but something for a quiet but hugely beefy workstation that’s not $9k per CPU)? Preferably more cores the better since my workload scales horizontally quite well (that’s why I looked at Ampere in the first place a while ago and almost did pull the trigger)

> has hyper-threading (!!!) meaning you get 384 threads

isn't SMT turned off in shared-tenant scenarios now due to security concerns

No, you can use core scheduling to assign both threads to the same tenant.