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Comment by wnevets | Hacker News Reader

If you're on windows you can easily turn them off with inspectre from grc [1]

On Linux kernel >=5.1.13 you can add mitigations=off kernel boot parameter to turn off all mitigations.

There are more granular parameters that are supported by all kernels implementing CPU mitigations: noibrs noibpb nopti nospectre_v2 nospectre_v1 l1tf=off nospec_store_bypass_disable no_stf_barrier mds=off mitigations=off

https://unix.stackexchange.com/questions/554908/disable-spec...

I have a test suite that went from 19 minutes to 8 with mitigations=off

which CPU?

Threadripper, 12-core 2920X

I don't think so.

I do lots of compiling at work and our compiler hasn't changed in 5+ years.

pre spectre my 8700k could do 20k lines/sec. Post spectre with mitigation it's about 10k, with them disabled it's about 15k.

There's clearly been some under the hood changes to windows beyond these optional? changes.

did you do a bios update or something you forgot about?

No bios update, but I wouldn't be surprised if windows shipped updated microcode or something.

I am trying to understand this: you are compiling programs on Windows?

Yes, our application compiles it's own sub applications. It is win32 software.

It looks like it doesn't work on my PC: if I run it with elevated privileges and toggle off protections, they're back on when I restart the app.

You will need to restart your PC for the changes to take effect and show in the app.

Oh OK thanks.

Fwiw a reboot didn't change anything!

Alternatively using registry edit: https://support.microsoft.com/en-us/help/4072698/windows-ser...

Does turning them off improve performance?

Yes, very significantly, especially on old CPUs that don’t have hardware mitigations.

I've read the word "mitigation" so much (not only here, and not only you; so this comment is not directed at you personally) that I only hear doublespeak now: when people say mitigation I immediately think of a slab of concrete in the back of my car to compensate for not having any brakes installed. Please recognize for what it is: a design failure that is pampered upon. A mitigation is not a solution, it lessens the impact of the failure mode that was identified. Afaik, if the flushes and changes actually work, it is not a mitigation but a workaround: the failure mode cannot occur anymore. Mitigation sounds better than workaround though (and is probably the reason it was choosen).

Mitigation and work around mean the same thing.

Not really: mitigation lessens the effect, workaround avoids the effect.

I don't think it turns off all mitigations. Only few of them.

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