netdev - Re: [PATCH v2 iwl-net 3/8] ice: replace synchronize_rcu with synchronize

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Date: Tue, 4 Jun 2024 12:49:54 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: "Nelson, Shannon" <shannon.nelson@....com>
CC: <intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>,
	<anthony.l.nguyen@...el.com>, <magnus.karlsson@...el.com>,
	<michal.kubiak@...el.com>, <larysa.zaremba@...el.com>
Subject: Re: [PATCH v2 iwl-net 3/8] ice: replace synchronize_rcu with
 synchronize_net

On Fri, May 31, 2024 at 04:49:01PM -0700, Nelson, Shannon wrote:
> On 5/29/2024 4:23 AM, Maciej Fijalkowski wrote:
> > 
> > Given that ice_qp_dis() is called under rtnl_lock, synchronize_net() can
> > be called instead of synchronize_rcu() so that XDP rings can finish its
> > job in a faster way. Also let us do this as earlier in XSK queue disable
> > flow.
> > 
> > Additionally, turn off regular Tx queue before disabling irqs and NAPI.
> > 
> > Fixes: 2d4238f55697 ("ice: Add support for AF_XDP")
> > Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> > ---
> >   drivers/net/ethernet/intel/ice/ice_xsk.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> > index 4f606a1055b0..e93cb0ca4106 100644
> > --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> > +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> > @@ -53,7 +53,6 @@ static void ice_qp_clean_rings(struct ice_vsi *vsi, u16 q_idx)
> >   {
> >          ice_clean_tx_ring(vsi->tx_rings[q_idx]);
> >          if (ice_is_xdp_ena_vsi(vsi)) {
> > -               synchronize_rcu();
> >                  ice_clean_tx_ring(vsi->xdp_rings[q_idx]);
> >          }
> 
> With only one statement left in the block you'll probably want to remove the
> {}'s

Thanks for catching this. To explain myself here, I was getting rid of a
patch which removes the XDP prog presence check altogether because it is a
false positive - we can't get into these queue pair disabling/enabling
functions if there is no XDP prog on interface. And the reason why I was
tossing this out of patch set was that it was not -net candidate.

Thanks again and will fix on v3.

> 
> sln
> 
> 
> >          ice_clean_rx_ring(vsi->rx_rings[q_idx]);
> > @@ -180,11 +179,12 @@ static int ice_qp_dis(struct ice_vsi *vsi, u16 q_idx)
> >                  usleep_range(1000, 2000);
> >          }
> > 
> > +       synchronize_net();
> > +       netif_tx_stop_queue(netdev_get_tx_queue(vsi->netdev, q_idx));
> > +
> >          ice_qvec_dis_irq(vsi, rx_ring, q_vector);
> >          ice_qvec_toggle_napi(vsi, q_vector, false);
> > 
> > -       netif_tx_stop_queue(netdev_get_tx_queue(vsi->netdev, q_idx));
> > -
> >          ice_fill_txq_meta(vsi, tx_ring, &txq_meta);
> >          err = ice_vsi_stop_tx_ring(vsi, ICE_NO_RESET, 0, tx_ring, &txq_meta);
> >          if (err)
> > --
> > 2.34.1
> > 
> > 
>