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SubjectRe: [PATCH] cpu/hotplug: Create SMT sysfs interface for all arches
On Sun, Mar 24, 2019 at 09:13:18PM +0100, Thomas Gleixner wrote:
> On Fri, 1 Mar 2019, Josh Poimboeuf wrote:
> > Make the /sys/devices/system/cpu/smt/* files available on all arches, so
> > user space has a consistent way to detect whether SMT is enabled.
> >
> > The 'control' file now shows 'notsupported' for architectures which
> > don't yet have CONFIG_HOTPLUG_SMT.
>
> I'm slowly crawling through my backlog ...
>
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -514,7 +514,8 @@ Description: Control Symetric Multi Threading (SMT)
> > "on" SMT is enabled
> > "off" SMT is disabled
> > "forceoff" SMT is force disabled. Cannot be changed.
> > - "notsupported" SMT is not supported by the CPU
> > + "notsupported" Runtime SMT toggling is not currently
> > + supported for the architecture
>
> Second thoughts. I'm not really convinced that changing the meaning of
> notsupported and in fact overloading it, is the right thing to do.
> notsupported means now:
>
> CPU does not support it - OR - architecture does not support it
>
> That's not pretty and we are surely not short of state space. There are
> several options for handling this:
>
> 1) Do not expose the state file, just expose the active file
>
> 2) Expose the state file, but return -ENOTSUPP or some other sensible error
> code
>
> 3) Expose the state file and let show return 'notimplemented' which is
> more accurate. That wouldn't even require to expand the state space
> enum. It just can be returned unconditionally.

Makes sense. I like #3. I can post another version.

--
Josh

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