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

[David Laight]

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.

-- David