Re: [dpdk-dev] [EXT] [PATCH v3 1/3] eal/arm64: add 128-bit atomic compare exchange

[Jerin Jacob Kollanukkaran <jerinj@marvell.com>]

> -----Original Message-----
> From: Phil Yang <phil.yang@arm.com>
> Sent: Friday, June 28, 2019 1:42 PM
> To: dev@dpdk.org
> Cc: thomas@monjalon.net; Jerin Jacob Kollanukkaran <jerinj@marvell.com>;
> hemant.agrawal@nxp.com; Honnappa.Nagarahalli@arm.com;
> gavin.hu@arm.com; nd@arm.com; gage.eads@intel.com
> Subject: [EXT] [PATCH v3 1/3] eal/arm64: add 128-bit atomic compare exchange
> 
> Add 128-bit atomic compare exchange on aarch64.
> 
> Signed-off-by: Phil Yang <phil.yang@arm.com>
> Tested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> ---
> v3:
> 1. Avoid duplication code with macro. (Jerin Jocob) 2. Make invalid memory
> order to strongest barrier. (Jerin Jocob) 3. Update
> doc/guides/prog_guide/env_abstraction_layer.rst. (Eads Gage) 4. Fix 32-bit x86
> builds issue. (Eads Gage) 5. Correct documentation issues in UT. (Eads Gage)
> 
>  .../common/include/arch/arm/rte_atomic_64.h        | 165
> +++++++++++++++++++++
>  .../common/include/arch/x86/rte_atomic_64.h        |  12 --
>  lib/librte_eal/common/include/generic/rte_atomic.h |  17 ++-
>  3 files changed, 181 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
> b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
> index 97060e4..2080c4d 100644
> --- a/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
> +++ b/lib/librte_eal/common/include/arch/arm/rte_atomic_64.h
> @@ -1,5 +1,6 @@
>  /* SPDX-License-Identifier: BSD-3-Clause
>   * Copyright(c) 2015 Cavium, Inc
> + * Copyright(c) 2019 Arm Limited
>   */
> 
>  #ifndef _RTE_ATOMIC_ARM64_H_
> @@ -14,6 +15,9 @@ extern "C" {
>  #endif
> 
>  #include "generic/rte_atomic.h"
> +#include <rte_branch_prediction.h>
> +#include <rte_compat.h>
> +#include <rte_debug.h>
> 
>  #define dsb(opt) asm volatile("dsb " #opt : : : "memory")  #define dmb(opt) asm
> volatile("dmb " #opt : : : "memory") @@ -40,6 +44,167 @@ extern "C" {
> 
>  #define rte_cio_rmb() dmb(oshld)
> 
> +/*------------------------ 128 bit atomic operations
> +-------------------------*/
> +
> +#define RTE_HAS_ACQ(mo) ((mo) != __ATOMIC_RELAXED && (mo) !=
> +__ATOMIC_RELEASE) #define RTE_HAS_RLS(mo) ((mo) == __ATOMIC_RELEASE
> || \
> +			 (mo) == __ATOMIC_ACQ_REL || \
> +			 (mo) == __ATOMIC_SEQ_CST)
> +
> +#define RTE_MO_LOAD(mo)  (RTE_HAS_ACQ((mo)) \
> +		? __ATOMIC_ACQUIRE : __ATOMIC_RELAXED) #define
> RTE_MO_STORE(mo)
> +(RTE_HAS_RLS((mo)) \
> +		? __ATOMIC_RELEASE : __ATOMIC_RELAXED)
> +
> +#ifdef __ARM_FEATURE_ATOMICS
> +#define __ATOMIC128_CAS_OP(cas_op_name, op_string)                          \
> +static inline rte_int128_t                                                  \
> +cas_op_name(rte_int128_t *dst, rte_int128_t old,                            \
> +		rte_int128_t updated)                                               \
> +{                                                                           \
> +	/* caspX instructions register pair must start from even-numbered
> +	 * register at operand 1.
> +	 * So, specify registers for local variables here.
> +	 */                                                                     \
> +	register uint64_t x0 __asm("x0") = (uint64_t)old.val[0];                \

I understand CASP limitation on register has to be even and odd.
Is there anyway to remove explicit x0 register allocation and
choose compiler to decide the register. Some reason with optimize(03)
gcc makes correctly but not clang.

Hardcoding to specific register makes compiler to not optimize the stuff,
especially if it is inline function.