Re: [PATCH] net/mlx5: setup RSS regardless of queue count

[Yongseok Koh <yskoh@mellanox.com>]

On Tue, Mar 20, 2018 at 01:26:08PM +0100, Nélio Laranjeiro wrote:
> On Mon, Mar 19, 2018 at 11:30:07AM -0500, Allain Legacy wrote:
> > From: Dahir Osman <dahir.osman@windriver.com>
> > 
> > In some environments it is desirable to have the NIC perform RSS
> > normally on the packet regardless of the number of queues configured.
> > The RSS hash result that is stored in the mbuf can then be used by
> > the application to make decisions about how to distribute workloads
> > to threads, secondary processes, or even virtual machines if the
> > application is a virtual switch.  This change to the mlx5 driver
> > aligns with how other drivers in the Intel family work.
> > 
> > Signed-off-by: Allain Legacy <allain.legacy@windriver.com>
> > ---
> >  drivers/net/mlx5/mlx5_rxq.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
> > index ff58c4921..e6b05b0ad 100644
> > --- a/drivers/net/mlx5/mlx5_rxq.c
> > +++ b/drivers/net/mlx5/mlx5_rxq.c
> > @@ -1028,7 +1028,8 @@ mlx5_priv_rxq_new(struct priv *priv, uint16_t idx, uint16_t desc,
> >  	      tmpl->rxq.crc_present ? "disabled" : "enabled",
> >  	      tmpl->rxq.crc_present << 2);
> >  	/* Save port ID. */
> > -	tmpl->rxq.rss_hash = priv->rxqs_n > 1;
> > +	tmpl->rxq.rss_hash = (!!(dev->data->dev_conf.rxmode.mq_mode &
> > +				 ETH_MQ_RX_RSS));
> >  	tmpl->rxq.port_id = dev->data->port_id;
> >  	tmpl->priv = priv;
> >  	tmpl->rxq.mp = mp;
> > -- 
> > 2.12.1
> 
> Unfortunately, is not enough to have a valid RSS hash result when the
> PMD has a single Rx queue, a little more work needs to be handled in the
> mlx5_flow.c engine to configure the hash field in Verbs Hash Rx queues
> when a single queues is being used.

It is good to have such feature like described in the commit message. And from
Allain's other email, it seems datapath of mlx5 ignores valid hash result from
HW for no reason if the number of queue is one. Allain, you wanted to fix that,
didn't you?

Nelio, can you please share a bit more idea of what should be done further in
mlx5_flow.c for this, so that Allain can come up with a right patch?


Thanks,
Yongseok