Re: [dpdk-dev] [PATCH] eal/ppc: remove fix of memory barrier for IBM POWER

["Chao Zhu" <chaozhu@linux.vnet.ibm.com>]

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Dekel£¬

To control the memory order for device memory, I think you should use 
rte_io_mb() instead of rte_mb(). This will generate correct result. rte_wmb() 
is used for system memory.

> -----Original Message-----
> From: Dekel Peled <dekelp@mellanox.com>
> Sent: Monday, March 18, 2019 8:58 PM
> To: chaozhu@linux.vnet.ibm.com
> Cc: yskoh@mellanox.com; shahafs@mellanox.com; dev@dpdk.org;
> orika@mellanox.com; thomas@monjalon.net; dekelp@mellanox.com;
> stable@dpdk.org
> Subject: [PATCH] eal/ppc: remove fix of memory barrier for IBM POWER
>
> From previous patch description: "to improve performance on PPC64, use light
> weight sync instruction instead of sync instruction."
>
> Excerpt from IBM doc [1], section "Memory barrier instructions":
> "The second form of the sync instruction is light-weight sync, or lwsync.
> This form is used to control ordering for storage accesses to system memory
> only. It does not create a memory barrier for accesses to device memory."
>
> This patch removes the use of lwsync, so calls to rte_wmb() and
> rte_rmb() will provide correct memory barrier to ensure order of accesses to
> system memory and device memory.
>
> [1] https://www.ibm.com/developerworks/systems/articles/powerpc.html
>
> Fixes: d23a6bd04d72 ("eal/ppc: fix memory barrier for IBM POWER")
> Cc: stable@dpdk.org
>
> Signed-off-by: Dekel Peled <dekelp@mellanox.com>
> ---
>  lib/librte_eal/common/include/arch/ppc_64/rte_atomic.h | 8 --------
>  1 file changed, 8 deletions(-)
>
> diff --git a/lib/librte_eal/common/include/arch/ppc_64/rte_atomic.h
> b/lib/librte_eal/common/include/arch/ppc_64/rte_atomic.h
> index ce38350..797381c 100644
> --- a/lib/librte_eal/common/include/arch/ppc_64/rte_atomic.h
> +++ b/lib/librte_eal/common/include/arch/ppc_64/rte_atomic.h
> @@ -63,11 +63,7 @@
>   * Guarantees that the STORE operations generated before the barrier
>   * occur before the STORE operations generated after.
>   */
> -#ifdef RTE_ARCH_64
> -#define	rte_wmb() asm volatile("lwsync" : : : "memory")
> -#else
>  #define	rte_wmb() asm volatile("sync" : : : "memory")
> -#endif
>
>  /**
>   * Read memory barrier.
> @@ -75,11 +71,7 @@
>   * Guarantees that the LOAD operations generated before the barrier
>   * occur before the LOAD operations generated after.
>   */
> -#ifdef RTE_ARCH_64
> -#define	rte_rmb() asm volatile("lwsync" : : : "memory")
> -#else
>  #define	rte_rmb() asm volatile("sync" : : : "memory")
> -#endif
>
>  #define rte_smp_mb() rte_mb()
>
> --
> 1.8.3.1