# SMT (Hyperthreading) and/or Multi-core scheduler support

## Cr0t

The kernel has an option for "SMT (Hyperthreading) scheduler support" and "Multi-core scheduler support". If you have a system with HT and physical cpus, do you select both?

I have been just selecting multi-core scheduler and all the cpus are being used and show up for that matter.

Any reason why SMT is still listed since multi-core finds the HT cpus as well?

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## Gusar

You should use SMT. Yeah, multi-core will work too, sorta, but the kernel will think all cores are equal. The cores are not equal with hyperthreading though, and SMT will make the kernel aware of that.

If you select both, the kernel will use SMT if it sees the machine has hyperthreading, and multi-core otherwise. It will not use both.

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## _______0

the answer is in the help tab. Hyperthreading is, exclusively, for pentium4s, the other for the rest.

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## Gusar

 *_______0 wrote:*   

> the answer is in the help tab. Hyperthreading is, exclusively, for pentium4s, the other for the rest.

 

Incorrect. Pentium 4 was the first processor that had hyperthreading, but Core i3/5/7 processors have it too.

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## nlsa8z6zoz7lyih3ap

Where does the amd fx-8350 fit into this?

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## _______0

I wasn't talking about hypeardthreading in cpus but at to which cpu that option applies to.

[ ] SMT (Hyperthreading) scheduler support

```
 SMT scheduler support improves the CPU scheduler's decision making

  when dealing with Intel Pentium 4 chips with HyperThreading at a

   cost of slightly increased overhead in some places. If unsure say

   N here.
```

So for AMD the second one:

[*] Multi-core scheduler support

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## Hu

Kernel help text, although useful, is sometimes out of date.  Do you have a more definitive reference for that feature applying only on Pentium4 chips?  I see nothing in the kernel source for SMT handling that appears to restrict it to Pentium4 chips.

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