> -----Original Message-----
> From: pbhagavat...@marvell.com <pbhagavat...@marvell.com>
> Sent: Monday, October 4, 2021 6:03 PM
> To: jer...@marvell.com; Ruifeng Wang <ruifeng.w...@arm.com>
> Cc: dev@dpdk.org; Pavan Nikhilesh <pbhagavat...@marvell.com>
> Subject: [dpdk-dev] [RFC] eal/arm: remove CASP constraints for GCC
>
> From: Pavan Nikhilesh <pbhagavat...@marvell.com>
>
> GCC now assigns even register pairs for CASP, the fix has also been
> backported to all stable releases of older GCC versions.
> Removing the manual register allocation allows GCC to inline the functions
> and pick optimal registers for performing CASP.
>
> Signed-off-by: Pavan Nikhilesh <pbhagavat...@marvell.com>
> ---
> lib/eal/arm/include/rte_atomic_64.h | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/lib/eal/arm/include/rte_atomic_64.h
> b/lib/eal/arm/include/rte_atomic_64.h
> index fa6f334c0d..f6f31ae777 100644
> --- a/lib/eal/arm/include/rte_atomic_64.h
> +++ b/lib/eal/arm/include/rte_atomic_64.h
> @@ -52,6 +52,7 @@ rte_atomic_thread_fence(int memorder)
> #define __LSE_PREAMBLE ""
> #endif
>
> +#if defined(__clang__)
> #define __ATOMIC128_CAS_OP(cas_op_name, op_string) \
> static __rte_noinline void \
> cas_op_name(rte_int128_t *dst, rte_int128_t *old, rte_int128_t updated)
> \
> @@ -76,6 +77,19 @@ cas_op_name(rte_int128_t *dst, rte_int128_t *old,
> rte_int128_t updated) \
> old->val[0] = x0; \
> old->val[1] = x1; \
> }
> +#else
> +#define __ATOMIC128_CAS_OP(cas_op_name, op_string) \
> +static __rte_always_inline void \
> +cas_op_name(rte_int128_t *dst, rte_int128_t *old, rte_int128_t updated)
> \
> +{ \
> + asm volatile( \
> + __LSE_PREAMBLE \
Change looks good.
One minor comment, gcc doesn't need this PREAMBLE.
Thanks,
Ruifeng
> + op_string " %[old], %H[old], %[upd], %H[upd], [%[dst]]" \
> + : [old] "+r"(old->int128) \
> + : [upd] "r"(updated.int128), [dst] "r"(dst) \
> + : "memory"); \
> +}
> +#endif
>
> __ATOMIC128_CAS_OP(__cas_128_relaxed, "casp")
> __ATOMIC128_CAS_OP(__cas_128_acquire, "caspa")
> --
> 2.17.1
