Re: [dpdk-dev] [PATCH 3/3] net/virtio: reject unsupported Rx multi queue modes

[Tiwei Bie <tiwei.bie@intel.com>]

On Wed, Oct 09, 2019 at 12:00:28PM +0300, Andrew Rybchenko wrote:
> On 10/9/19 11:43 AM, Tiwei Bie wrote:
> > On Wed, Oct 09, 2019 at 11:04:38AM +0300, Andrew Rybchenko wrote:
> > > On 10/8/19 8:46 AM, Tiwei Bie wrote:
> > > > On Tue, Oct 01, 2019 at 04:44:31PM +0100, Andrew Rybchenko wrote:
> > > > > From: Dilshod Urazov <Dilshod.Urazov@oktetlabs.ru>
> > > > > 
> > > > > This driver supports none of DCB, RSS or VMDQ modes,
> > > > > therefore must check and return error if configured incorrectly.
> > > > > 
> > > > > Fixes: c1f86306a026 ("virtio: add new driver")
> > > > > Cc: stable@dpdk.org
> > > > > 
> > > > > Signed-off-by: Dilshod Urazov <Dilshod.Urazov@oktetlabs.ru>
> > > > > Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
> > > > > ---
> > > > >    drivers/net/virtio/virtio_ethdev.c | 7 +++++++
> > > > >    1 file changed, 7 insertions(+)
> > > > > 
> > > > > diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
> > > > > index 7261109dd..0af4fc392 100644
> > > > > --- a/drivers/net/virtio/virtio_ethdev.c
> > > > > +++ b/drivers/net/virtio/virtio_ethdev.c
> > > > > @@ -2071,6 +2071,13 @@ virtio_dev_configure(struct rte_eth_dev *dev)
> > > > >    	PMD_INIT_LOG(DEBUG, "configure");
> > > > >    	req_features = VIRTIO_PMD_DEFAULT_GUEST_FEATURES;
> > > > > +	if (rxmode->mq_mode != ETH_MQ_RX_NONE) {
> > > > > +		PMD_DRV_LOG(ERR,
> > > > > +			"Unsupported Rx multi queue mode %d",
> > > > > +			rxmode->mq_mode);
> > > > > +		return -EINVAL;
> > > > > +	}
> > > > We need similar checks for Tx as well.
> > > OK, I'll add.
> > > 
> > > However, I'm not 100% sure about RSS. Yes, I know that virtio has
> > > no RSS configuration support, but it looks possible to have multi queue
> > > in vhost-net case.
> > Yeah, it's possible to have MQ in virtio.
> > The RSS support in virtio is still WIP.
> > https://github.com/oasis-tcs/virtio-spec/issues/48
> 
> Thanks for the link. So, may be ETH_MQ_RX_RSS should be accepted
> as well, but attempts to configure RSS rejected?
> Yes, it is a bit strange to accept RSS with empty rss_hf etc, but
> at least it is exactly what net/virtio can do.
> 
> And one more thought...
> It looks like if more than one Rx queue is configured, mq_mode must
> be ETH_MQ_RX_RSS and must not be ETH_MQ_RX_NONE.

Some apps in DPDK will set mq_mode to ETH_MQ_RX_NONE while
enabling multiple queue pairs, e.g.:

https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test/test_link_bonding.c#L137
https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test/test_link_bonding.c#L181-L182
https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test/test_link_bonding.c#L3938-L3948

Testpmd will also set mq_mode to ETH_MQ_RX_NONE when multiple
Rx queues are enabled but rss_hf is empty:

https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test-pmd/testpmd.c#L2935-L2938
https://github.com/DPDK/dpdk/blob/5b5bb56532fd5dea5d6260c0a0e405c0e32da2a0/app/test-pmd/testpmd.c#L2945-L2948
(the flow_type_rss_offloads reported by virtio-PMD is zero)

My understanding is that, setting mq_mode to ETH_MQ_RX_NONE means
no method is enforced on how to route packets to MQs.
It looks that ETH_MQ_RX_NONE is the best fit for virtio currently.