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Does simultaneous multithreading still make sense?

codeblueprint.co.uk

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Re: Does simultaneous multithreading still make sense?

#12

Post by clarry »

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 think of are not running CPUs with SMT.

Re: Does simultaneous multithreading still make sense?

#15

Post by grzm »

maweki wrote: post #14

I wish that acronyms would be written out if they have multiple meanings in the computer context. My first thought was "how can satisfiability modulo theory ever not make sense?"

The first paragraph of the article makes it very clear what they’re referring to:

> Whatever machine you’re reading this on, it’s highly likely that not all of the CPUs shown by the OS are actually physical processors. That’s because most modern processors use simultaneous multithreading (SMT) to improve performance by executing tasks in parallel.

Re: Does simultaneous multithreading still make sense?

#17

Post by metaphor »

saagarjha wrote: post #10
metaphor wrote: post #9

FYSA, SMT in this context is simultaneous multithreading a.k.a. hyperthreading , not surface mount technology . Hardware folks can safely move on.

And not “Satisfiability modulo theories” either, it seems. I would never recommend people to “move on” from an interesting article, though.

Agreed.

At first glance, I genuinely thought this was going to be a pitch for yet another fragile additive manufacturing toy with narrow usecase, or a new process that enables IPC-7092 designs on the cheap.

Re: Does simultaneous multithreading still make sense?

#18

Post by kijin »

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.

Re: Does simultaneous multithreading still make sense?

#19

Post by Fronzie »

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.

For computational tasks, I've seen SMT give a roughly 50% performance increase compared to not using SMT on the same machine.

Much of that depends on how 'regular' the executions are. A highly optimized FFT or BLAS routine will benefit less than a sparse matrix computation, where part of the time is spent in indexing, rather than floating point operations.

Re: Does simultaneous multithreading still make sense?

#20

Post by callmeal »

maweki wrote: post #14

I wish that acronyms would be written out if they have multiple meanings in the computer context. My first thought was "how can satisfiability modulo theory ever not make sense?"

I thought it was Surface Mount Technology and was wondering what kind of replacement was being proposed.
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