How can I enable Hyper-Threading again for Linux 5.14? I don’t have vulnerable hardware so want maximum performance.
I guess you search this:
https://wiki.archlinux.org/title/Improving_performance#Turn_off_CPU_exploit_mitigations
On Intel CPUs HT is disabled sometimes cause of security.
I don’t believe that… xD
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@Tribble
Hi!
Did you saw How to provide good information ?
What is pre-history: how did you lost it?
Under which circumstances did you have the HT?
“Sometimes”? May be you have a bit more details on that?
Sorry, but I don’t go into details here. It really depends on the CPU and when it was built… etc.
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Is SMT being disable by default starting with Kernel 5.14?
I can’t seem to find any news of this.
This is the closest I could find, but it doesn’t appear to really affect desktop users:
https://www.phoronix.com/scan.php?page=news_item&px=Linux-5.14-Core-Sched-Off
Yes I have it enabled by default. Great stuff.
cat /sys/devices/system/cpu/smt/active
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sudo dmidecode -t processor | grep --color HTT
HTT (Multi-threading)
Was it not enabled in 5.13 and earlier? On 5.13 I get the same results: SMT/HTT is enabled by default
No idea. The only thing I didn’t touch yet was mitigations, because you have to edit grub and apply.
Honestly, I’d leave that alone. The real-world gains are negligible. SMT/HTT is what makes the biggest difference. Disabling the mitigations against exploits and vulnerabilities barely improves performance, beyond what you gain by enabling SMT/HTT (which is default in recent kernels.) Not worth the risk in my opinion.
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SMT/HTT disabled, mitigations enabled = notable negative performance impact -
SMT/HTT enabled, mitigations enabled = near optimal performance -
SMT/HTT enabled, mitigations disabled = barely faster than the above combination (not worth the risk)
The question to me is “was HT disabled anyway in any kernel?”. I don’t believe so.
According to some sources, hyper-threading only works on one core, doesn’t matter if you have 4 or 6 cores, but they will still say double threads. So how’s that exactly?
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