Re: [PATCH v3 0/9] s390: Improve this_cpu operations

[Yang Shi]

On 5/21/26 3:23 AM, David Laight wrote:
> On Wed, 20 May 2026 17:23:37 -0700
> Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> > On 5/20/26 3:34 PM, David Laight wrote:
> ..
> > > > So it seems have more overhead than the percpu page table approach IIUC.
> > > > We don't need all the steps with percpu page table. And there is no
> > > > penalty for migration.
> > > This code looks like it relies on 'page zero' already being percpu.
> > > So it probably isn't really that different.
> > > Some values like the 'preemption disable count' and 'current' could be
> > > (maybe are?) written into page zero to give fast access.
> > I don't quite get what you mean about 'page zero'.
> 'page zero' is (at least for some cpu) the memory that can be accessed
> using a small offset embedded in the instruction.
> This is equivalent to using offsets from an 'always zero' %r0.
>
> The code relies on the accesses to 960(%r0) being per-cpu.

Thank you. Heiko also elaborated it.

Yang

> -- David