RFC: Adding a hw.features[2] sysctl

John Baldwin jhb at freebsd.org
Mon Jan 14 06:32:37 PST 2008

On Saturday 12 January 2008 11:16:27 pm Joe Marcus Clarke wrote:
> I find it would be useful to have the list of CPU features available via
> a sysctl.  Currently, he only ways to get this information are to have
> linprocfs mounted, or parse dmesg.boot (if it exists).  Attached are
> patches to add hw.features and hw.features2 sysctls for i386 and amd64
> (where a list of CPU features is applicable).  The results are identical
> to the Features and Features2 strings from dmesg:
> hw.features2: 0x41d<SSE3,RSVD2,MON,DS_CPL,CNXT-ID>
> hw.features:
> Comments?

I would put this under machdep. rather than hw. since it is x86-specific.

I also think having feature and feature2 might be a bit odd as you have to
query two different nodes.  Someday there might be a features3 when
features2 runs out of bits and then all the apps would have to be updated
again perhaps.  Maybe something like:


Or maybe if you use named nodes like this you could do dev.cpu.X.FPU=1,
dev.cpu.X.VME=1, etc. (possibly dev.cpu.X.feature.FPU=1, etc.)

John Baldwin

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