RE: [PATCH v2] eal: introduce atomics abstraction

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> Sent: Wednesday, 8 February 2023 22.44
> 
> Introduce atomics abstraction that permits optional use of standard C11
> atomics when meson is provided the new enable_stdatomics=true option.
> 
> Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> ---

Looks good. A few minor suggestions about implementation only.

With or without suggested modifications,

Acked-by: Morten Brørup <mb@smartsharesystems.com>


>  config/meson.build                     | 11 ++++
>  lib/eal/arm/include/rte_atomic_32.h    |  6 ++-
>  lib/eal/arm/include/rte_atomic_64.h    |  6 ++-
>  lib/eal/include/generic/rte_atomic.h   | 96
> +++++++++++++++++++++++++++++++++-
>  lib/eal/loongarch/include/rte_atomic.h |  6 ++-
>  lib/eal/ppc/include/rte_atomic.h       |  6 ++-
>  lib/eal/riscv/include/rte_atomic.h     |  6 ++-
>  lib/eal/x86/include/rte_atomic.h       |  8 ++-
>  meson_options.txt                      |  2 +
>  9 files changed, 139 insertions(+), 8 deletions(-)
> 
> diff --git a/config/meson.build b/config/meson.build
> index 26f3168..25dd628 100644
> --- a/config/meson.build
> +++ b/config/meson.build
> @@ -255,6 +255,17 @@ endif
>  # add -include rte_config to cflags
>  add_project_arguments('-include', 'rte_config.h', language: 'c')
> 
> +stdc_atomics_enabled = get_option('enable_stdatomics')
> +dpdk_conf.set('RTE_STDC_ATOMICS', stdc_atomics_enabled)
> +
> +if stdc_atomics_enabled
> +if cc.get_id() == 'gcc' or cc.get_id() == 'clang'
> +    add_project_arguments('-std=gnu11', language: 'c')
> +else
> +    add_project_arguments('-std=c11', language: 'c')
> +endif
> +endif
> +
>  # enable extra warnings and disable any unwanted warnings
>  # -Wall is added by default at warning level 1, and -Wextra
>  # at warning level 2 (DPDK default)
> diff --git a/lib/eal/arm/include/rte_atomic_32.h
> b/lib/eal/arm/include/rte_atomic_32.h
> index c00ab78..7088a12 100644
> --- a/lib/eal/arm/include/rte_atomic_32.h
> +++ b/lib/eal/arm/include/rte_atomic_32.h
> @@ -34,9 +34,13 @@
>  #define rte_io_rmb() rte_rmb()
> 
>  static __rte_always_inline void
> -rte_atomic_thread_fence(int memorder)
> +rte_atomic_thread_fence(rte_memory_order memorder)
>  {
> +#ifdef RTE_STDC_ATOMICS
> +	atomic_thread_fence(memorder);
> +#else
>  	__atomic_thread_fence(memorder);
> +#endif
>  }
> 
>  #ifdef __cplusplus
> diff --git a/lib/eal/arm/include/rte_atomic_64.h
> b/lib/eal/arm/include/rte_atomic_64.h
> index 6047911..7f02c57 100644
> --- a/lib/eal/arm/include/rte_atomic_64.h
> +++ b/lib/eal/arm/include/rte_atomic_64.h
> @@ -38,9 +38,13 @@
>  #define rte_io_rmb() rte_rmb()
> 
>  static __rte_always_inline void
> -rte_atomic_thread_fence(int memorder)
> +rte_atomic_thread_fence(rte_memory_order memorder)
>  {
> +#ifdef RTE_STDC_ATOMICS
> +	atomic_thread_fence(memorder);
> +#else
>  	__atomic_thread_fence(memorder);
> +#endif
>  }
> 
>  /*------------------------ 128 bit atomic operations -----------------
> --------*/
> diff --git a/lib/eal/include/generic/rte_atomic.h
> b/lib/eal/include/generic/rte_atomic.h
> index f5c49a9..392d928 100644
> --- a/lib/eal/include/generic/rte_atomic.h
> +++ b/lib/eal/include/generic/rte_atomic.h
> @@ -110,6 +110,100 @@
> 
>  #endif /* __DOXYGEN__ */
> 
> +#ifdef RTE_STDC_ATOMICS
> +
> +#if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 201112L ||
> defined(__STDC_NO_ATOMICS__)
> +#error compiler does not support C11 standard atomics
> +#else
> +#include <stdatomic.h>
> +#endif
> +
> +#define __rte_atomic _Atomic
> +
> +typedef int rte_memory_order;

I would prefer enum for rte_memory_order:

typedef enum {
    rte_memory_order_relaxed = memory_order_relaxed,
    rte_memory_order_consume = memory_order_consume,
    rte_memory_order_acquire = memory_order_acquire,
    rte_memory_order_release = memory_order_release,
    rte_memory_order_acq_rel = memory_order_acq_rel,
    rte_memory_order_seq_cst = memory_order_seq_cst
} rte_memory_order;

> +
> +#define rte_memory_order_relaxed memory_order_relaxed
> +#define rte_memory_order_consume memory_order_consume
> +#define rte_memory_order_acquire memory_order_acquire
> +#define rte_memory_order_release memory_order_release
> +#define rte_memory_order_acq_rel memory_order_acq_rel
> +#define rte_memory_order_seq_cst memory_order_seq_cst
> +
> +#define rte_atomic_store_explicit(obj, desired, order) \
> +	atomic_store_explicit(obj, desired, order)
> +
> +#define rte_atomic_load_explicit(obj, order) \
> +	atomic_load_explicit(obj, order)
> +
> +#define rte_atomic_exchange_explicit(obj, desired, order) \
> +	atomic_exchange_explicit(obj, desired, order)
> +
> +#define rte_atomic_compare_exchange_strong_explicit(obj, expected,
> desired, success, fail) \
> +	atomic_compare_exchange_strong_explicit(obj, expected, desired,
> success, fail)
> +
> +#define rte_atomic_compare_exchange_weak_explicit(obj, expected,
> desired, success, fail) \
> +	atomic_compare_exchange_weak_explicit(obj, expected, desired,
> success, fail)
> +
> +#define rte_atomic_fetch_add_explicit(obj, arg, order) \
> +	atomic_fetch_add_explicit(obj, arg, order)
> +
> +#define rte_atomic_fetch_sub_explicit(obj, arg, order) \
> +	atomic_fetch_sub_explicit(obj, arg, order)
> +
> +#define rte_atomic_fetch_or_explicit(obj, arg, order) \
> +	atomic_fetch_or_explicit(obj, arg, order)
> +
> +#define rte_atomic_fetch_xor_explicit(obj, arg, order) \
> +	atomic_fetch_xor_explicit(obj, arg, order)
> +
> +#define rte_atomic_fetch_and_explicit(obj, arg, order) \
> +	atomic_fetch_and_explicit(obj, arg, order)
> +
> +#else
> +
> +#define __rte_atomic
> +
> +typedef int rte_memory_order;
> +
> +#define rte_memory_order_relaxed __ATOMIC_RELAXED
> +#define rte_memory_order_consume __ATOMIC_CONSUME
> +#define rte_memory_order_acquire __ATOMIC_ACQUIRE
> +#define rte_memory_order_release __ATOMIC_RELEASE
> +#define rte_memory_order_acq_rel __ATOMIC_ACQ_REL
> +#define rte_memory_order_seq_cst __ATOMIC_SEQ_CST

Prefer enum for rte_memory_order:

typedef enum {
    rte_memory_order_relaxed = __ATOMIC_RELAXED,
    rte_memory_order_consume = __ATOMIC_CONSUME,
    rte_memory_order_acquire = __ATOMIC_ACQUIRE,
    rte_memory_order_release = __ATOMIC_RELEASE,
    rte_memory_order_acq_rel = __ATOMIC_ACQ_REL,
    rte_memory_order_seq_cst = __ATOMIC_SEQ_CST
} rte_memory_order;

> +
> +#define rte_atomic_store_explicit(obj, desired, order) \
> +	__atomic_store_n(obj, desired, order)
> +
> +#define rte_atomic_load_explicit(obj, order) \
> +	__atomic_load_n(obj, order)
> +
> +#define rte_atomic_exchange_explicit(obj, desired, order) \
> +	__atomic_exchange_n(obj, desired, order)
> +
> +#define rte_atomic_compare_exchange_strong_explicit(obj, expected,
> desired, success, fail) \
> +	__atomic_compare_exchange_n(obj, expected, desired, 0, success,
> fail)

The type of the "weak" parameter to __atomic_compare_exchange_n() is bool, not int, so use "false" instead of 0. There is probably no practical difference, so I'll leave it up to you.

You might need to include <stdbool.h> for this... I haven't checked.

> +
> +#define rte_atomic_compare_exchange_weak_explicit(obj, expected,
> desired, success, fail) \
> +	__atomic_compare_exchange_n(obj, expected, desired, 1, success,
> fail)

Same as above: Use "true" instead of 1.

> +
> +#define rte_atomic_fetch_add_explicit(obj, arg, order) \
> +	__atomic_fetch_add(obj, arg, order)
> +
> +#define rte_atomic_fetch_sub_explicit(obj, arg, order) \
> +	__atomic_fetch_sub(obj, arg, order)
> +
> +#define rte_atomic_fetch_or_explicit(obj, arg, order) \
> +	__atomic_fetch_or(obj, arg, order)
> +
> +#define rte_atomic_fetch_xor_explicit(obj, arg, order) \
> +	__atomic_fetch_xor(obj, arg, order)
> +
> +#define rte_atomic_fetch_and_explicit(obj, arg, order) \
> +	__atomic_fetch_and(obj, arg, order)
> +
> +#endif
> +
>  /**
>   * Compiler barrier.
>   *
> @@ -123,7 +217,7 @@
>  /**
>   * Synchronization fence between threads based on the specified memory
> order.
>   */
> -static inline void rte_atomic_thread_fence(int memorder);
> +static inline void rte_atomic_thread_fence(rte_memory_order memorder);
> 
>  /*------------------------- 16 bit atomic operations -----------------
> --------*/
> 
> diff --git a/lib/eal/loongarch/include/rte_atomic.h
> b/lib/eal/loongarch/include/rte_atomic.h
> index 3c82845..66aa0c8 100644
> --- a/lib/eal/loongarch/include/rte_atomic.h
> +++ b/lib/eal/loongarch/include/rte_atomic.h
> @@ -35,9 +35,13 @@
>  #define rte_io_rmb()	rte_mb()
> 
>  static __rte_always_inline void
> -rte_atomic_thread_fence(int memorder)
> +rte_atomic_thread_fence(rte_memory_order memorder)
>  {
> +#ifdef RTE_STDC_ATOMICS
> +	atomic_thread_fence(memorder);
> +#else
>  	__atomic_thread_fence(memorder);
> +#endif
>  }
> 
>  #ifdef __cplusplus
> diff --git a/lib/eal/ppc/include/rte_atomic.h
> b/lib/eal/ppc/include/rte_atomic.h
> index 663b4d3..a428a83 100644
> --- a/lib/eal/ppc/include/rte_atomic.h
> +++ b/lib/eal/ppc/include/rte_atomic.h
> @@ -38,9 +38,13 @@
>  #define rte_io_rmb() rte_rmb()
> 
>  static __rte_always_inline void
> -rte_atomic_thread_fence(int memorder)
> +rte_atomic_thread_fence(rte_memory_order memorder)
>  {
> +#ifdef RTE_STDC_ATOMICS
> +	atomic_thread_fence(memorder);
> +#else
>  	__atomic_thread_fence(memorder);
> +#endif
>  }
> 
>  /*------------------------- 16 bit atomic operations -----------------
> --------*/
> diff --git a/lib/eal/riscv/include/rte_atomic.h
> b/lib/eal/riscv/include/rte_atomic.h
> index 4b4633c..3c203a9 100644
> --- a/lib/eal/riscv/include/rte_atomic.h
> +++ b/lib/eal/riscv/include/rte_atomic.h
> @@ -40,9 +40,13 @@
>  #define rte_io_rmb()	asm volatile("fence ir, ir" : : : "memory")
> 
>  static __rte_always_inline void
> -rte_atomic_thread_fence(int memorder)
> +rte_atomic_thread_fence(rte_memory_order memorder)
>  {
> +#ifdef RTE_STDC_ATOMICS
> +	atomic_thread_fence(memorder);
> +#else
>  	__atomic_thread_fence(memorder);
> +#endif
>  }
> 
>  #ifdef __cplusplus
> diff --git a/lib/eal/x86/include/rte_atomic.h
> b/lib/eal/x86/include/rte_atomic.h
> index f2ee1a9..02d8b12 100644
> --- a/lib/eal/x86/include/rte_atomic.h
> +++ b/lib/eal/x86/include/rte_atomic.h
> @@ -87,12 +87,16 @@
>   * used instead.
>   */
>  static __rte_always_inline void
> -rte_atomic_thread_fence(int memorder)
> +rte_atomic_thread_fence(rte_memory_order memorder)
>  {
> -	if (memorder == __ATOMIC_SEQ_CST)
> +	if (memorder == rte_memory_order_seq_cst)
>  		rte_smp_mb();
>  	else
> +#ifdef RTE_STDC_ATOMICS
> +		atomic_thread_fence(memorder);
> +#else
>  		__atomic_thread_fence(memorder);
> +#endif
>  }
> 
>  /*------------------------- 16 bit atomic operations -----------------
> --------*/
> diff --git a/meson_options.txt b/meson_options.txt
> index 0852849..acbcbb8 100644
> --- a/meson_options.txt
> +++ b/meson_options.txt
> @@ -46,6 +46,8 @@ option('mbuf_refcnt_atomic', type: 'boolean', value:
> true, description:
>         'Atomically access the mbuf refcnt.')
>  option('platform', type: 'string', value: 'native', description:
>         'Platform to build, either "native", "generic" or a SoC. Please
> refer to the Linux build guide for more information.')
> +option('enable_stdatomics', type: 'boolean', value: false,
> description:
> +       'enable use of standard C11 atomics.')
>  option('enable_trace_fp', type: 'boolean', value: false, description:
>         'enable fast path trace points.')
>  option('tests', type: 'boolean', value: true, description:
> --
> 1.8.3.1
>