Re: [PATCH] net/mlx5: return RSS hash result in mbuf

["Nélio Laranjeiro" <nelio.laranjeiro@6wind.com>]

Hi Bruce,

On Tue, Sep 27, 2016 at 03:11:10PM +0100, Bruce Richardson wrote:
> On Wed, Sep 14, 2016 at 10:16:05AM +0200, Nelio Laranjeiro wrote:
> > Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
> > ---
> >  drivers/net/mlx5/mlx5_rxq.c  | 1 +
> >  drivers/net/mlx5/mlx5_rxtx.c | 6 +++++-
> >  drivers/net/mlx5/mlx5_rxtx.h | 2 ++
> >  3 files changed, 8 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
> > index f6f4315..65c264b 100644
> > --- a/drivers/net/mlx5/mlx5_rxq.c
> > +++ b/drivers/net/mlx5/mlx5_rxq.c
> > @@ -926,6 +926,7 @@ rxq_ctrl_setup(struct rte_eth_dev *dev, struct rxq_ctrl *rxq_ctrl,
> >  		.rxq = {
> >  			.elts_n = log2above(desc),
> >  			.mp = mp,
> > +			.rss_hash = !!(priv->rxqs_n > 1),
> >  		},
> 
> Two comments on this:
> 1. I don't think the !! is needed, since this is a comparison which will result
>    in 0 or 1, rather than an int value that needs to be clamped to those values.

Ok for this one.

> 2. Why limit the use of RSS to when there is more than one RX queues? Sometimes
>    it might be useful to have a precomputed hash for a packet even when not
>    spreading packets among RX queues. For example, when using a single RX queue,
>    but doing a hash table lookup for each packet, the RSS value could be used
>    as the lookup hash.
> 
> /Bruce

ConnectX-4 NICs does not return a hash value for a single queue as
software does not request RSS in this situation, that is why it is not
filled.

I will send a v2 to also fix a bug discovered since concerning the hash
result which is not retrieve from the right place when Completion Queue
Entry is compressed.

Regards,

-- 
Nélio Laranjeiro
6WIND