Re: [PATCH v2 26/28] arm64/sve: Add documentation

Dave Martin
2017-10-09T09:49:32Z

On Mon, Oct 09, 2017 at 10:34:25AM +0100, Alex Bennée wrote:
>
> Dave Martin <Dave.Martin@arm.com> writes:
>
> > On Fri, Oct 06, 2017 at 04:43:43PM +0100, Szabolcs Nagy wrote:
> >> On 31/08/17 18:00, Dave Martin wrote:
> >> > +9. System runtime configuration
> >> > +--------------------------------
> >> > +
> >> > +* To mitigate the ABI impact of expansion of the signal frame, a policy
> >> > + mechanism is provided for administrators, distro maintainers and developers
> >> > + to set the default vector length for userspace processes:
> >> > +
> >> > +/proc/cpu/sve_default_vector_length
> >>
> >>
> >> elsewhere in the patch series i see
> >>
> >> /proc/sys/abi/sve_default_vector_length
> >>
> >> is this supposed to be the same?
> >
> > Good spot, thanks!
> >
> > /proc/cpu/ was the old location: they should both say /proc/abi/.
> > I'll fix it.
>
> Isn't /sys (or rather sysfs) the preferred location for modern control
> knobs that mirror the kernels object model or is SVE a special case for
> extending /proc?

I couldn't figure out which kernel object this maps to. There's no
device, no driver. This isn't even per-cpu.

sysctl is already used for similar knobs to this one, so I followed that
precedent -- though if someone argues strongly enough it could be
changed.

Are there already examples of arch controls like this in sysfs? I
wasn't aware of any, but I didn't look all that hard...

Cheers
---Dave