[PATCH] riscv/futex: Optimize atomic cmpxchg
Andrea Parri
parri.andrea at gmail.com
Wed Nov 13 11:15:05 PST 2024
On Wed, Nov 13, 2024 at 10:33:21AM -0800, Davidlohr Bueso wrote:
> Remove redundant release/acquire barriers, optimizing the lr/sc sequence
> to provide conditional RCsc synchronization, per the RVWMO.
>
> Signed-off-by: Davidlohr Bueso <dave at stgolabs.net>
> ---
> arch/riscv/include/asm/futex.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/futex.h b/arch/riscv/include/asm/futex.h
> index fc8130f995c1..72be100afa23 100644
> --- a/arch/riscv/include/asm/futex.h
> +++ b/arch/riscv/include/asm/futex.h
> @@ -85,7 +85,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
>
> __enable_user_access();
> __asm__ __volatile__ (
> - "1: lr.w.aqrl %[v],%[u] \n"
> + "1: lr.w %[v],%[u] \n"
> " bne %[v],%z[ov],3f \n"
> "2: sc.w.aqrl %[t],%z[nv],%[u] \n"
> " bnez %[t],1b \n"
atomic_cmpxchg() uses yet another scheme, but this does also look good
to me: FWIW,
Reviewed-by: Andrea Parri <parri.andrea at gmail.com>
Andrea
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