[External] Re: [PATCH RFC] riscv: use gp to save percpu offset

[yunhui cui]

Hi Christoph,


On Sat, Aug 24, 2024 at 9:57 AM Christoph Lameter (Ampere)
<cl at gentwo.org> wrote:
>
> On Sat, 24 Aug 2024, Yunhui Cui wrote:
>
> > Compared to directly fetching the per-CPU offset from memory (or cache),
> > using the global pointer (gp) to store the per-CPU offset can save one
> > memory access.
>
> Yes! That is a step in the right direction.
>
> Is there something like gp relative addressing so that we can do loads
> and stores relative to gp as well?
>
> Are there atomics that can do read modify write relative to GP? That would
> get  you to comparable per cpu efficiency to x86. x86 can do relative
> addressing and RMV in one instruction which allows one to drop the preempt
> enable/disable since one instruction cannot be interrupted.

Your suggestion is excellent. If conditions permit, we can indeed move
closer to the x86 architecture.

Thanks,
Yunhui