Re: [dpdk-dev] [PATCH] lib: move rte_ring read barrier to correct location

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

Hi ,

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Juhamatti Kuusisaari
> Sent: Monday, July 11, 2016 11:21 AM
> To: dev@dpdk.org
> Subject: [dpdk-dev] [PATCH] lib: move rte_ring read barrier to correct location
> 
> Fix the location of the rte_ring data dependency read barrier.
> It needs to be called before accessing indexed data to ensure
> that the data itself is guaranteed to be correctly updated.
> 
> See more details at kernel/Documentation/memory-barriers.txt
> section 'Data dependency barriers'.


Any explanation why?
>From my point smp_rmb()s are on the proper places here :)
Konstantin

> 
> Signed-off-by: Juhamatti Kuusisaari <juhamatti.kuusisaari@coriant.com>
> ---
>  lib/librte_ring/rte_ring.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
> index eb45e41..a923e49 100644
> --- a/lib/librte_ring/rte_ring.h
> +++ b/lib/librte_ring/rte_ring.h
> @@ -662,9 +662,10 @@ __rte_ring_mc_do_dequeue(struct rte_ring *r, void **obj_table,
>                                               cons_next);
>         } while (unlikely(success == 0));
> 
> +       rte_smp_rmb();
> +
>         /* copy in table */
>         DEQUEUE_PTRS();
> -       rte_smp_rmb();
> 
>         /*
>          * If there are other dequeues in progress that preceded us,
> @@ -746,9 +747,10 @@ __rte_ring_sc_do_dequeue(struct rte_ring *r, void **obj_table,
>         cons_next = cons_head + n;
>         r->cons.head = cons_next;
> 
> +       rte_smp_rmb();
> +
>         /* copy in table */
>         DEQUEUE_PTRS();
> -       rte_smp_rmb();
> 
>         __RING_STAT_ADD(r, deq_success, n);
>         r->cons.tail = cons_next;
> --
> 2.9.0
> 
> 
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