[dpdk-dev] [PATCH] net/mlx5: setup RSS regardless of queue count

[Nélio Laranjeiro]

On Tue, Mar 20, 2018 at 04:07:11PM -0700, Yongseok Koh wrote:
> 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 at 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 at 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.

Single queue means no RSS, it is not the datapath which ignore it, it is
the control plane which does not configure it.

> Allain, you wanted to fix that, didn't you?

>From the patch above, it seems :)

> 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?

The engine is not trivial as it needs to convert flow API to Verbs flows
which the restrictions from the MLX5 kernel driver.
Trying to give instructions ends by writing it down directly as I need
to test them to see if it does not break your requirements also.

Allain,  I will finalise this patch (today) and make some test, I'll
contact you once it is finish to see if the behavior you expect is
reached.

Thanks,

-- 
Nélio Laranjeiro
6WIND