With AMD Zen 4, It's Surprisingly Not Worthwhile Disabling CPU Security Mitigations

[skeevy420]

What's odd or fishy? Overly hardcore hardware mitigations making software mitigations moot seems logical enough.

[ssokolow]

That's the most counter-intuitive thing I've ever seen. All other benchmarks of the past showed that mitigations=off much improved perf at the expense of security. So does this imply AMD designed Zen 4 with the assumption of mitigation=on as a means of protecting users from themselves and disabling will cost you perf if you do? Carrot + stick?

Maybe they tuned the branch predictor to expect the patterns embodied by the mitigations. Mispredictions could explain it being worse when you turn them off.

[ridge]

That's great news!

[EvilHowl]

AMD has probably tweaked the hardware itself and the microcode to react better to the kernel behaviour when mitigations are enabled, which makes all the sense in the world given that most people will run the kernel at default settings.

If you know that some kernel paths are going to behave in an unoptimal or strange way, you can prepare the silicon to react as good as it can to it. Of course, if you disable all mitigations, the kernel will not behave as it is supposed to do at stock settings and the CPU will underperform, even if it's supposed to work faster that way. Think of it as a branch misprediction.

It's not fishy at all. I expect Intel to do the same on Rocket Lake.

[creative]

No you are not going to see any performance boost turning off mitigation's, lets just put it this way... Zen 4 and Raptor Lake are so fast that GPU's are actually bottle necking the CPU's. I thought my 5800x was ludicrous speed. We are now in a CPU performance territory where the newest CPU's coming out are absolutely space balls, mega maid is going from suck to blow, that's how fast they are.

Kindest courtesy,

Dark Helmet

[rabcor]

Press X to doubt.

Mitigations on should not be increasing performance.

[creative]

Press X to doubt.

Mitigations on should not be increasing performance.

AHAHAH Trailer Park Boys.

[andyprough]

LOL, Ubuntu. Where up is down and down is up. You should stick to real distros Michael, not these play things.

[david-nk]

AMD has probably tweaked the hardware itself and the microcode to react better to the kernel behaviour when mitigations are enabled, which makes all the sense in the world given that most people will run the kernel at default settings.

That doesn't explain why browser performance is down by 40%. The browser shouldn't spend enough time in kernel mode for any kernel performance differences to make much of an impact. That definitely requires further investigation.

[ezst036]

Wasn't one of the benefits of Zen 4 that some/most of these vulnerabilities were addressed at the hardware level?

Bump for repeat. I would like to know if others read this somewhere also, and if this what happened.

If these vulnerabilities are addressed at the hardware level, that would explain a lot.