OpenBSD Disabling SMT / Hyper Threading Due To Security Concerns

[kpedersen]

I trust these guys in their choice because they have generally proven to be smarter than most other developers.

Besides, it looks like they have added a kernel tunable to return SMT. Unlike the Gnome 3 crowd, these guys know about choice harhar.

[Weasel]

This is crazy. What's next? Disabling everything for "security" reasons?

Reminds me of Wayland.

[caligula]

SMT was just a hack to cover the fact that branch prediction misses in the long-pipeline "NetBurst" ( fire whoever came up with that name ) architecture were punishing performance. The proper solution would be to abandon the NetBurst architecture, which they did ( returned to the PIII architecture, but called it 'Core' ), but then brought bits of NetBurst back for some reason? Probably so they could flog dual-core systems as quad-core. Personally I disable SMT because it's horrible for realtime scheduling.

It's as much hack as any CPU architecture optimization. SMT can be great for filling the pipeline - the P4 implementation was crap, but look at IBM's POWER with 4/8-way SMT. It's not the only thing that messes up realtime processing. If you really want a deterministic pipeline, you'd need an in-order CPU without caches, TLBs, or other dynamic speedups. You'd probably also use a real time patched kernel, which might further hurt throughput in server processing.

[Venemo]

Why just disable Hyper-threading? Why not disable the entire CPU? That is the only way to make sure it does not execute any malicious code!

[Jeroen]

Or you can just turn off SMT in the BIOS... Even laptop have this option.

[Weasel]

Or you can just turn off SMT in the BIOS... Even laptop have this option.

That requires user input and knowledge, also choice, which is bad!

Remember these days you have to treat the user as a moron, a mobile muppet, who clicks (sorry i mean taps) on everything and then demands "protection". So they'd better do it for him!

/s

[Vistaus]

Next step : Burn your cpu and say " Good riddance "

https://www.youtube.com/watch?v=poiEC_kPk40

[Staffan]

OpenBSD isn't exactly focused on high performance computing anyway. With their security focus it makes sense for them to do this, at least in a default install. If the user then can choose to enable it it should be OK.

[PluMGMK]

HT is an abomination. I ended up disabling it on my work PC some time ago because of all the array calculations in Excel that were failing for no apparent reason…

[Leopard]

https://www.youtube.com/watch?v=poiEC_kPk40

Yeah , you can say that way too.