Re: [dpdk-dev] [PATCH v2 0/4] vhost: add missing barriers, move prefetching

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Dec 19, 2018 at 09:21:09AM +0100, Maxime Coquelin wrote:
> This series adds missing read barriers after reading avail index
> for split ring and desc flags for packed ring.
> 
> Also, it turns out that some descriptors prefetching are either
> badly placed, or useless, last part of the series fixes that.
> 
> With the series applied, I get between 0 and 4% gain depending
> on the benchmark (testpmd txonly/rxonly/io).
> 
> Thanks to Jason for reporting the missing read barriers.

Acked-by: Michael S. Tsirkin <mst@redhat.com>

But I wonder what effect this has on ARM where RMB isn't a NOP.
Ilya do you happen to have any data?

> Changes since v1:
> =================
> - Drop volatile removal patch (Ilya)
> - Improve commit messages for RMB patches (Ilya)
> 
> Maxime Coquelin (4):
>   vhost: enforce avail index and desc read ordering
>   vhost: enforce desc flags and content read ordering
>   vhost: prefetch descriptor after the read barrier
>   vhost: remove useless prefetch for packed ring descriptor
> 
>  lib/librte_vhost/virtio_net.c | 27 ++++++++++++++++++++++-----
>  1 file changed, 22 insertions(+), 5 deletions(-)
> 
> -- 
> 2.17.2