Re: [Intel-wired-lan] [PATCH v2 net] ixgbe: allow to increase MTU to some extent with XDP enabled

[Jason Xing]

On Mon, Jan 30, 2023 at 11:09 PM Maciej Fijalkowski
<maciej.fijalkowski@xxxxxxxxx> wrote:
>
> On Fri, Jan 27, 2023 at 08:20:18PM +0800, Jason Xing wrote:
> > From: Jason Xing <kernelxing@xxxxxxxxxxx>
> >
> > I encountered one case where I cannot increase the MTU size directly
> > from 1500 to 2000 with XDP enabled if the server is equipped with
> > IXGBE card, which happened on thousands of servers in production
> > environment.
>

> You said in this thread that you've done several tests - what were they?

Tests against XDP are running on the server side when MTU varies from
1500 to 3050 (not including ETH_HLEN, ETH_FCS_LEN and VLAN_HLEN) for a
few days.
I choose the iperf tool to test the maximum throughput and observe the
behavior when the machines are under greater pressure. Also, I use
netperf to send different size packets to the server side with
different modes (TCP_RR/_STREAM) applied.

> Now that you're following logic from other drivers, have you tested 3k MTU

Sure, the maximum MTU size users could set is 3050 (which is 3072 - 14
- 4 - 4 in ixgbe_change_mtu() function).

> against XDP? Because your commit msg still refer to 2k as your target. If
> 3k is fine then i would reflect that in the subject of the patch.

I will modify the title and body message both.

>
> >
> > This patch follows the behavior of changing MTU as i40e/ice does.
> >
> > Referrences:
> > commit 23b44513c3e6f ("ice: allow 3k MTU for XDP")
> > commit 0c8493d90b6bb ("i40e: add XDP support for pass and drop actions")
> >
> > Link: https://lore.kernel.org/lkml/20230121085521.9566-1-kerneljasonxing@xxxxxxxxx/
>
> Why do you share a link to v1 here?

I originally intended to let maintainers trace the previous
discussion. Well, I'm going to remove the link.

>
> You're also missing Fixes: tag, as you're targetting the net tree.
>

I'll do it in the v3 patch.

Thanks,
Jason

> > Signed-off-by: Jason Xing <kernelxing@xxxxxxxxxxx>
> > ---
> > v2:
> > 1) change the commit message.
> > 2) modify the logic when changing MTU size suggested by Maciej and Alexander.
> > ---
> >  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 25 ++++++++++++-------
> >  1 file changed, 16 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > index ab8370c413f3..2c1b6eb60436 100644
> > --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > @@ -6777,6 +6777,18 @@ static void ixgbe_free_all_rx_resources(struct ixgbe_adapter *adapter)
> >                       ixgbe_free_rx_resources(adapter->rx_ring[i]);
> >  }
> >
> > +/**
> > + * ixgbe_max_xdp_frame_size - returns the maximum allowed frame size for XDP
> > + * @adapter - device handle, pointer to adapter
> > + */
> > +static int ixgbe_max_xdp_frame_size(struct ixgbe_adapter *adapter)
> > +{
> > +     if (PAGE_SIZE >= 8192 || adapter->flags2 & IXGBE_FLAG2_RX_LEGACY)
> > +             return IXGBE_RXBUFFER_2K;
> > +     else
> > +             return IXGBE_RXBUFFER_3K;
> > +}
> > +
> >  /**
> >   * ixgbe_change_mtu - Change the Maximum Transfer Unit
> >   * @netdev: network interface device structure
> > @@ -6788,18 +6800,13 @@ static int ixgbe_change_mtu(struct net_device *netdev, int new_mtu)
> >  {
> >       struct ixgbe_adapter *adapter = netdev_priv(netdev);
> >
> > -     if (adapter->xdp_prog) {
> > +     if (ixgbe_enabled_xdp_adapter(adapter)) {
> >               int new_frame_size = new_mtu + ETH_HLEN + ETH_FCS_LEN +
> >                                    VLAN_HLEN;
> > -             int i;
> > -
> > -             for (i = 0; i < adapter->num_rx_queues; i++) {
> > -                     struct ixgbe_ring *ring = adapter->rx_ring[i];
> >
> > -                     if (new_frame_size > ixgbe_rx_bufsz(ring)) {
> > -                             e_warn(probe, "Requested MTU size is not supported with XDP\n");
> > -                             return -EINVAL;
> > -                     }
> > +             if (new_frame_size > ixgbe_max_xdp_frame_size(adapter)) {
> > +                     e_warn(probe, "Requested MTU size is not supported with XDP\n");
> > +                     return -EINVAL;
> >               }
> >       }
> >
> > --
> > 2.37.3
> >
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