AMD's SMT vs. Intel's Hyper-Threading

[Marzipan]

this is an interesting write up. in short, AMD's SMT is better than Intel's HT, but requires more power. I wonder how AMD's SMT would fare if they power limited the Ryzen so it couldn't go beyond what Intel's CPU consumes.

Hyper-Threading on Intel is More Efficient than SMT on AMD Ryzen CPUs: But...

Recently, it was discovered that Intel plans to do away with hyper-threading on its future processors (Lunar Lake, if not Arrow). Simultaneous Multi-Threading, known as Hyper-Threading on Intel platforms, has been around for a long time. It works by alternating the execution units of a CPU...

www.hardwaretimes.com

 

[Bond007]

I will have to give this a read later on.

I seem to remember that AMD's implementation had more of the the 2 threads independent within a "core" but that is all I recall...we will see what I learn after reading.

 

[gingerbee]

this really isn't surprising to me when you consider just how much longer Intel has had a version of SMT/hyper-threading, correct me if I am wrong but AMD has only implemented SMT with the Ryzen series CPU so only 7 years( not sure if SMT was on server chips earlier then Ryzern), whereas Intel has had hyper-threading since all the way back to the Pentium 4 days I think.

What I wonder is why in some cases Intel CPUs do worse with HT enabled, is it because Intel utilizes their thread per core better, but I think it also shows Ryzen may in the future have more than 2 threads per core, was there not some talk about a chip having 4 threads per-core " I may have heard it about another chip not sure"

 

[Izerous]

was there not some talk about a chip having 4 threads per-core " I may have heard it about another chip not sure"

been rumors of quad threads on CPUs for a long time, I don't expect to see it any time soon. From what I recall there was a performance hit since the core's attention was now split 4 different ways (management overhead etc). There might be something in the server space by now but not mainstream market....

However since Intel bit with the whole Big/Little design like arm chips and stuff do it makes me wonder if we took an Intel...
-8P + 8E = 24 threads

Killed off the E cores and swapped them for 2 quad threaded cores...
-8P + 2Quad = 24 threads

I bet the performance would be comparible but the manufacturing cost would likely be cheaper.

 

[gingerbee]

thanks very much for that, I did not think of it in that way.

 

[Izerous]

POWER9 - Microarchitectures - IBM - WikiChip

POWER9 is IBM's successor to POWER8, a 14 nm microarchitecture for Power-based server microprocessors first introduced in the 2nd half of 2017. POWER9-based processors are branded under the POWER family.

en.wikichip.org

IBM power 9 was the one that I recall reading about it has SMT4 (4 threads per core) & SMT8 (8 threads per core).

 

[Bond007]

Interesting. That was a much shorter read than I was expecting.

So summary from this article is that amd uses way less power per core (with or without SMT) than intel, but there is a decent increase in performance and power consumption with SMT enabled. Intel uses notably more power per core, but there is very little change in performance or power consumption with hyperthreading enabled.

I did not hear the rumour that intel may ditch hyperthreading moving forward, but I am not surprised given their push to e-cores for heavily threaded tasks and the fact that hyper threading has less/no benefit in lightly threaded uses...save "p-core" die space by getting ride of hyperthreading and use that space for more "e-cores" to offset in threaded tasks. Makes sense at a glance given the articles highlight of their strenghts/weaknesses.

 

[Bond007]

been rumors of quad threads on CPUs for a long time, I don't expect to see it any time soon. From what I recall there was a performance hit since the core's attention was now split 4 different ways (management overhead etc). There might be something in the server space by now but not mainstream market....

However since Intel bit with the whole Big/Little design like arm chips and stuff do it makes me wonder if we took an Intel...
-8P + 8E = 24 threads

Killed off the E cores and swapped them for 2 quad threaded cores...
-8P + 2Quad = 24 threads

I bet the performance would be comparible but the manufacturing cost would likely be cheaper.

I think IBM is the only one I heard of running more than 2 threads (per your other post). If the article has any truth to it I think it may go the otherway on cores...

6P+14E = 20 threads? No idea really...just throwing numbers around if they ditch hyperthreading and increase E cores.

 

[MARSTG]

been rumors of quad threads on CPUs for a long time, I don't expect to see it any time soon.

Power 7, IBM had 4 SMT threads since the Power 7 CPU, so it is out there.

 

[gingerbee]

What I got from that is AMD may be better off going more SMT per core than using a BigLittle design like Intel has, I also thought I read they were tinkering with a design to do so. Yup it seems they have been messing around with the idea of SMT4 IE 4 threads per core no clue if this was just a rumor or not, I mean if they can make it work it could be useful.

Edit well not AMD but I guess other have been working on it

Hot Chips 2020: Marvell Details ThunderX3 CPUs - Up to 60 Cores Per Die, 96 Dual-Die in 2021

www.anandtech.com