Re: [PATCH v6 21/21] Documentation: arm64: describe asymmetric 32-bit support

[Will Deacon]

On Fri, May 21, 2021 at 06:37:21PM +0100, Qais Yousef wrote:
> On 05/18/21 10:47, Will Deacon wrote:
> > Document support for running 32-bit tasks on asymmetric 32-bit systems
> > and its impact on the user ABI when enabled.
> > 
> > Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> > ---
> >  .../admin-guide/kernel-parameters.txt         |   3 +
> >  Documentation/arm64/asymmetric-32bit.rst      | 149 ++++++++++++++++++
> >  Documentation/arm64/index.rst                 |   1 +
> >  3 files changed, 153 insertions(+)
> >  create mode 100644 Documentation/arm64/asymmetric-32bit.rst
> > 
> 
> [...]
> 
> > +Cpusets
> > +-------
> > +
> > +The affinity of a 32-bit task may include CPUs that are not explicitly
> > +allowed by the cpuset to which it is attached. This can occur as a
> > +result of the following two situations:
> > +
> > +  - A 64-bit task attached to a cpuset which allows only 64-bit CPUs
> > +    executes a 32-bit program.
> > +
> > +  - All of the 32-bit-capable CPUs allowed by a cpuset containing a
> > +    32-bit task are offlined.
> > +
> > +In both of these cases, the new affinity is calculated according to step
> > +(2) of the process described in `execve(2)`_ and the cpuset hierarchy is
> > +unchanged irrespective of the cgroup version.
> 
> nit: Should we call out that we're breaking cpuset-v1 behavior? Don't feel
> strongly about it.

I think the text is pretty clear that the new behaviour documented here
applies to cpuset-v1 and I wouldn't say we're breaking anything as we're not
changing any of the existing behaviours.

Will