* tip-bot2 for Uros Bizjak <tip-bot2@xxxxxxxxxxxxx> wrote:
> The following commit has been merged into the x86/percpu branch of tip:
>
> Commit-ID: 0539084639f3835c8d0b798e6659ec14a266b4f1
> Gitweb: https://git.kernel.org/tip/0539084639f3835c8d0b798e6659ec14a266b4f1
> Author: Uros Bizjak <ubizjak@xxxxxxxxx>
> AuthorDate: Wed, 20 Mar 2024 09:30:40 +01:00
> Committer: Ingo Molnar <mingo@xxxxxxxxxx>
> CommitterDate: Wed, 20 Mar 2024 12:29:02 +01:00
>
> x86/percpu: Convert this_percpu_xchg_op() from asm() to C code, to generate better code
>
> Rewrite percpu_xchg_op() using generic percpu primitives instead
> of using asm. The new implementation is similar to local_xchg() and
> allows the compiler to perform various optimizations: e.g. the
> compiler is able to create fast path through the loop, according
> to likely/unlikely annotations in percpu_try_cmpxchg_op().
So, while at it, there's two other x86 percpu code generation details I was
wondering about:
1)
Right now it's GCC-only:
config CC_HAS_NAMED_AS
def_bool CC_IS_GCC && GCC_VERSION >= 120100
Because we wanted to create a stable core of known-working functionality.
I suppose we have already established that with the current merge window,
so it might be time to expand it.
Clang claims to be compatible:
https://releases.llvm.org/9.0.0/tools/clang/docs/LanguageExtensions.html
"You can also use the GCC compatibility macros __seg_fs and __seg_gs for the
same purpose. The preprocessor symbols __SEG_FS and __SEG_GS indicate their
support."
I haven't tried it yet though.
2)
Also, is the GCC_VERSION cutoff accurate - are previous GCC versions
known-buggy, or was it primarily a risk-reduction cutoff?
Thanks,
Ingo
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