> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Friday, October 26, 2018 3:47 AM
> To: Xing, Beilei <beilei.x...@intel.com>; Zhang, Qi Z <qi.z.zh...@intel.com>
> Cc: dev@dpdk.org; sta...@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v2] net/i40e: fix Rx instability with vector
> mode
>
>
> Hi,
>
> >
> > Previously, there is instability during vector Rx if descriptor number
> > is not power of 2, e.g. process hang and some Rx packets are
> > unexpectedly empty. That's because vector Rx mode assumes Rx
> > descriptor number is power of 2 when doing bit mask.
> > This patch allows vector mode only when the number of Rx descriptor is
> > power of 2.
> >
> > Fixes: 8e109464c022 ("i40e: allow vector Rx and Tx usage")
> > Fixes: a3c83a2527e1 ("net/i40e: enable runtime queue setup")
> > Cc: sta...@dpdk.org
> >
> > Signed-off-by: Beilei Xing <beilei.x...@intel.com>
> > ---
> >
> > v2 changes:
> > - rx_vec_allowed is global configuration, avoid overwrite.
> >
> > doc/guides/nics/i40e.rst | 7 +++++++
> > drivers/net/i40e/i40e_rxtx.c | 13 ++++++++++++-
> > 2 files changed, 19 insertions(+), 1 deletion(-)
> >
> > diff --git a/doc/guides/nics/i40e.rst b/doc/guides/nics/i40e.rst index
> > ab3928a..bfacbd1 100644
> > --- a/doc/guides/nics/i40e.rst
> > +++ b/doc/guides/nics/i40e.rst
> > @@ -172,6 +172,13 @@ Runtime Config Options
> >
> > -w 84:00.0,use-latest-supported-vec=1
> >
> > +Vector RX Pre-conditions
> > +~~~~~~~~~~~~~~~~~~~~~~~~
> > +For Vector RX it is assumed that the number of descriptor rings will
> > +be a power of 2. With this pre-condition, the ring pointer can easily
> > +scroll back to the head after hitting the tail without a conditional
> > +check. In addition Vector RX can use this assumption to do a bit mask
> using ``ring_size - 1``.
> > +
> > Driver compilation and testing
> > ------------------------------
> >
> > diff --git a/drivers/net/i40e/i40e_rxtx.c
> > b/drivers/net/i40e/i40e_rxtx.c index a827456..f6dcca0 100644
> > --- a/drivers/net/i40e/i40e_rxtx.c
> > +++ b/drivers/net/i40e/i40e_rxtx.c
> > @@ -1735,10 +1735,14 @@ i40e_dev_rx_queue_setup_runtime(struct
> rte_eth_dev *dev,
> > * i40e_set_rx_function.
> > */
> > ad->rx_bulk_alloc_allowed = true;
> > - ad->rx_vec_allowed = true;
> > dev->data->scattered_rx = use_scattered_rx;
> > if (use_def_burst_func)
> > ad->rx_bulk_alloc_allowed = false;
> > + /**
> > + * Vector mode is allowed only when number of Rx queue
> > + * descriptor is a power of 2.
> > + */
> > + ad->rx_vec_allowed = !(rxq->nb_rx_desc & (rxq->nb_rx_desc - 1));
> > i40e_set_rx_function(dev);
> > return 0;
> > }
>
> I think this is not complete - if it is not the first function, we have to
> do:
> If (if (ad->rx_vec_allowed && (rxq->nb_rx_desc & (rxq->nb_rx_desc - 1) != 0)
> {
> PMD_DRV_LOG(ERR, ...);
> return -EINVAL;
> }
Yes, we should prevent downgrade if the device is already running.
>
> BTW, here and below why not to use rte_is_power_of_2()?
> Konstantin
>
> > @@ -1811,6 +1815,13 @@ i40e_dev_rx_queue_setup(struct rte_eth_dev
> *dev,
> > return -EINVAL;
> > }
> >
> > + /**
> > + * Vector mode is allowed only when number of Rx queue
> > + * descriptor is a power of 2.
> > + */
> > + if (ad->rx_vec_allowed)
> > + ad->rx_vec_allowed = !(nb_desc & (nb_desc - 1));
Looks like we are not able to get back to vec mode once some queue is set to no
power of 2, even if all queues has been re-setup to power of 2 again.
Seems we still need to check all other queue's configure here.
> > +
> > /* Free memory if needed */
> > if (dev->data->rx_queues[queue_idx]) {
> > i40e_dev_rx_queue_release(dev->data->rx_queues[queue_idx]);
>
>
>
>
>
>
