Re: [PATCH v1] LoongArch: Use current_stack_pointer in current_pt_regs()

[Huacai Chen]

On Thu, Aug 13, 2026 at 5:55 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
>
> On 2026/8/13 下午5:32, Huacai Chen wrote:
> > Hi, Tiezhu,
> >
> > On Thu, Aug 13, 2026 at 5:05 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
> >>
> >> The current implementation of current_pt_regs() relies on the compiler
> >> __builtin_frame_address(0). This introduces an unnecessary dependency
> >> on the frame pointer register, which forces the compiler to generate
> >> redundant prologue and epilogue code, create a larger stack frame, and
> >> perform redundant memory operations to preserve the frame pointer even
> >> in functions where it is otherwise unnecessary.
> >>
> >> Optimize this by switching to current_stack_pointer, which explicitly
> >> maps to the hardware stack pointer register. This allows the compiler
> >> to compute the stack alignment directly from the natively maintained
> >> $sp register, completely eliminating the overhead of preserving and
> >> restoring the frame pointer on the stack memory.
> >>
> >> As a prominent example, this optimization significantly improves the
> >> hot-path function copy_thread(). A localized disassembly comparison
> >> of copy_thread() illustrates the elimination of the frame pointer,
> >> the reduction of stack frame size from 48 bytes down to 32 bytes,
> >> and a more compact epilogue path:
> > 3 instructions and 16 bytes stack space. There is improvement, but not
> > "significantly".
>
> I used "significantly" from the perspective of hot-path sensitivity,
> but I agree that 3 instructions and 16 bytes might be inaccurate.
>
> If the code itself looks good to you, please feel free to update the
> commit message as you see fit when applying.
>
> Alternatively, let me know if you prefer me to send a v2 with a more
> accurate description.
Unnecessary, I will modify it.

Huacai

>
> Thanks,
> Tiezhu
>