RE: [PATCH] ring: add cache guard after ring elements table

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

Hi Morten,

> Added cache guard after the table holding the ring elements, to avoid
> false sharing conflicts caused by next-line hardware prefetchers when
> accessing elements at the end of the ring table.

I don't see any harm with it, and in theory it might help in some cases...
Though I wonder how real is that problem?
Did you ever observe such contention to happen?

> Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
> ---
>  lib/ring/rte_ring.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/lib/ring/rte_ring.c b/lib/ring/rte_ring.c
> index f10050a1c4..9ccc62cd42 100644
> --- a/lib/ring/rte_ring.c
> +++ b/lib/ring/rte_ring.c
> @@ -73,8 +73,11 @@ rte_ring_get_memsize_elem(unsigned int esize, unsigned
> int count)
>  		return -EINVAL;
>  	}
> 
> +	static_assert(sizeof(struct rte_ring) ==
> RTE_CACHE_LINE_ROUNDUP(sizeof(struct rte_ring)),
> +			"Size of struct rte_ring not cache line aligned");
>  	sz = sizeof(struct rte_ring) + (ssize_t)count * esize;
>  	sz = RTE_ALIGN(sz, RTE_CACHE_LINE_SIZE);
> +	sz += RTE_CACHE_GUARD_LINES * RTE_CACHE_LINE_SIZE;
>  	return sz;
>  }
> 
> --
> 2.43.0