Hacker News new | ask | show | jobs
by derefr 406 days ago
> if I boot with clearcpuid=smap (not for prod use!), larger reads go significantly faster. On both Intel and AMD CPUs interestingly.

Is there a page anywhere that collects these sorts of "turn the whole hardware security layer off" switches that can be flipped to get better throughput out of modern x86 CPUs, when your system has no real attack surface to speak of (e.g. air-gapped single-tenant HPC)?
1 comments
the8472 405 days ago
On the kernel side there's a boot parameter for all of them: mitigations=off Software that was compiled with additional fences may have to be recompiled to remove them.

https://www.kernel.org/doc/html/latest/admin-guide/kernel-pa...

link
starspangled 405 days ago
mitigations=off disables workarounds for bugs or "mis-features" in the CPU that could be exploited to bypass OS security measures.

smap is an OS security measure, and so does not get disabled by mitigations=off. smap can be pretty draining for certain IO performance though. IMO it should be more well-known or covered by a more obvious option.

Linux kernel developers are really bad at defining and naming options like this.

link