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Does simultaneous multithreading still make sense?

codeblueprint.co.uk

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Re: Does simultaneous multithreading still make sense?

#21

Post by esotericn »

clarry wrote: post #12

In the linked article about ghk's talk, you find this tidbit: "If you're not using a supported distro, or a stable long-term kernel, you have an insecure system. It's that simple. All those embedded devices out there, that are not updated, totally easy to break." Is he still talking about SMT, or just poor security of Linux in general? I'm wondering about this since "all those embedded devices out there" that I can t…

Tons of stuff like NUC's used as digital displays, kiosks, etc, everywhere. I'd be surprised if even half of that was on a proper update path.

Embedded isn't just like, microcontrollers. Think about all the times you've seen a BSOD on a billboard.

Re: Does simultaneous multithreading still make sense?

#22

Post by kijin »

pjmlp wrote: post #7
altmind wrote: post #5

Of course SMT makes sense. Why would it not be? Article says that thats because ppl only count the threads in their "cpuinfo" output and get the wrong impression? Intel vulnerabilities are not SMT vulnerabilities per-se, they are side channel attacks on a specific SMT implementation.

Some of them happen to be shared across all CPU vendors.

Which, now that they are known, can be fixed in future iterations of the technology. Just because Intel won't (or can't) fix their damn products doesn't mean that others won't.

Re: Does simultaneous multithreading still make sense?

#23

Post by pjmlp »

kijin wrote: post #22
pjmlp wrote: post #7

Earlier quoted context omitted.

Some of them happen to be shared across all CPU vendors.

Which, now that they are known, can be fixed in future iterations of the technology. Just because Intel won't (or can't) fix their damn products doesn't mean that others won't.

It also doesn't mean others will fix their damn products.

And even if they do, it doesn't mean anyone will replace existing hardware already deployed into production.

Re: Does simultaneous multithreading still make sense?

#25

Post by kijin »

pjmlp wrote: post #23
kijin wrote: post #22

Earlier quoted context omitted.

Which, now that they are known, can be fixed in future iterations of the technology. Just because Intel won't (or can't) fix their damn products doesn't mean that others won't.

It also doesn't mean others will fix their damn products. And even if they do, it doesn't mean anyone will replace existing hardware already deployed into production.

Sure, there's no guarantee, but that's not a particularly good reason to write off SMT wholesale.

People who already have Intel CPUs in production aren't just going to turn off hyper-threading, either, regardless of what we say about whether or not future products should support it.

Re: Does simultaneous multithreading still make sense?

#26

Post by rythie »

Intel i5 desktop chips don’t have hyper-threading (SMT) and haven’t for the 10 years they’ve been available. Typically the i7 variant of the same CPU has been about £100 more (roughly 50%). The point about only 5% extra die space makes no difference to the consumer, as there is/was quite a high cost premium on desktops for that feature. Now Intel has removed hyper-threading from most of it’s i7 desktop chips, and you get 2 extra cores over the i5 version instead.

Re: Does simultaneous multithreading still make sense?

#27

Post by NightlyDev »

kijin wrote: post #18
toast0 wrote: post #4

In my mind, SMT made more sense when core counts were low. These days, desktop use cases can more often run out of threads to run than places to run them. Server use cases can often run more threads, but it might not be useful to run 32 cpu threads if your NICs can only properly run 16 queues.

There's no direct correlation between NIC queues and CPU threads. The days of dedicating one thread to each incoming connection and/or HTTP request are long behind us, not to mention there are many tasks that require a lot of processing with little to no network activity.

That's not true. NIC queues and CPUs are still very important to get good performance on servers by pinning different queues to different cores.

Re: Does simultaneous multithreading still make sense?

#28

Post by baybal2 »

rythie wrote: post #26

Intel i5 desktop chips don’t have hyper-threading (SMT) and haven’t for the 10 years they’ve been available. Typically the i7 variant of the same CPU has been about £100 more (roughly 50%). The point about only 5% extra die space makes no difference to the consumer, as there is/was quite a high cost premium on desktops for that feature. Now Intel has removed hyper-threading from most of it’s i7 desktop chips, and you…

Desktop cores are tiny today in comparison to all other useless stuff put on die like "AI" accelerators and such.

That is even worse in mobile chips. All people call Intel cores to be oversized, but they need to look at up to date die shots. All cores combined can be less than a half of the die area.

Re: Does simultaneous multithreading still make sense?

#29

Post by kijin »

NightlyDev wrote: post #27
kijin wrote: post #18

Earlier quoted context omitted.

There's no direct correlation between NIC queues and CPU threads. The days of dedicating one thread to each incoming connection and/or HTTP request are long behind us, not to mention there are many tasks that require a lot of processing with little to no network activity.

That's not true. NIC queues and CPUs are still very important to get good performance on servers by pinning different queues to different cores.

Only if your workload involves passing around a lot of network traffic (e.g. a load balancer) or is highly latency-sensitive.

I've got backend servers that routinely max out 32c/64t CPUs but push so little traffic that replacing the NIC with a cell phone modem would make no discernible difference. There are many types of server workloads where the NIC is not the bottleneck at all, so the parent's argument that low NIC queue counts make high CPU core counts useless is false.

Re: Does simultaneous multithreading still make sense?

#30

Post by tyingq »

rythie wrote: post #26

Intel i5 desktop chips don’t have hyper-threading (SMT) and haven’t for the 10 years they’ve been available. Typically the i7 variant of the same CPU has been about £100 more (roughly 50%). The point about only 5% extra die space makes no difference to the consumer, as there is/was quite a high cost premium on desktops for that feature. Now Intel has removed hyper-threading from most of it’s i7 desktop chips, and you…

"Intel i5 desktop chips don’t have hyper-threading (SMT) and haven’t for the 10 years they’ve been available."

That's mostly true, though there have been a few desktop i5 processors with hyperthreads.

Like: https://ark.intel.com/content/www/us/en/ark/products/43546/i...

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