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Date: Fri, 4 Feb 2022 20:26:58 -0800 From: Eric Dumazet <edumazet@...gle.com> To: Jakub Kicinski <kuba@...nel.org> Cc: Eric Dumazet <eric.dumazet@...il.com>, "David S . Miller" <davem@...emloft.net>, netdev <netdev@...r.kernel.org> Subject: Re: [PATCH net-next 1/2] net: typhoon: implement ndo_features_check method On Fri, Feb 4, 2022 at 7:52 PM Jakub Kicinski <kuba@...nel.org> wrote: > > On Thu, 3 Feb 2022 10:02:26 -0800 Eric Dumazet wrote: > > From: Eric Dumazet <edumazet@...gle.com> > > > > Instead of disabling TSO if MAX_SKB_FRAGS > 32, implement > > ndo_features_check() method for this driver. > > > > If skb has more than 32 frags, use the following heuristic: > > > > 1) force GSO for gso packets. > > 2) Otherwise force linearization. > > > > Most locally generated packets will use a small number > > of fragments anyway. > > > > For forwarding workloads, we can limit gro_max_size at ingress, > > we might also implement gro_max_segs if needed. > > > > Signed-off-by: Eric Dumazet <edumazet@...gle.com> > > --- > > drivers/net/ethernet/3com/typhoon.c | 23 ++++++++++++++++++----- > > 1 file changed, 18 insertions(+), 5 deletions(-) > > > > diff --git a/drivers/net/ethernet/3com/typhoon.c b/drivers/net/ethernet/3com/typhoon.c > > index 8aec5d9fbfef2803c181387537300502a937caf0..67b1a1f439d841ed0ed0f620e9477607ac6e2fae 100644 > > --- a/drivers/net/ethernet/3com/typhoon.c > > +++ b/drivers/net/ethernet/3com/typhoon.c > > @@ -138,11 +138,6 @@ MODULE_PARM_DESC(use_mmio, "Use MMIO (1) or PIO(0) to access the NIC. " > > module_param(rx_copybreak, int, 0); > > module_param(use_mmio, int, 0); > > > > -#if defined(NETIF_F_TSO) && MAX_SKB_FRAGS > 32 > > -#warning Typhoon only supports 32 entries in its SG list for TSO, disabling TSO > > -#undef NETIF_F_TSO > > -#endif > > - > > #if TXLO_ENTRIES <= (2 * MAX_SKB_FRAGS) > > #error TX ring too small! > > #endif > > @@ -2261,9 +2256,27 @@ typhoon_test_mmio(struct pci_dev *pdev) > > return mode; > > } > > > > +#if MAX_SKB_FRAGS > 32 > > +static netdev_features_t typhoon_features_check(struct sk_buff *skb, > > + struct net_device *dev, > > + netdev_features_t features) > > +{ > > + if (skb_shinfo(skb)->nr_frags > 32) { > > + if (skb_is_gso(skb)) > > + features &= ~NETIF_F_GSO_MASK; > > + else > > + features &= ~NETIF_F_SG; > > Should we always clear SG? If we want to make the assumption that > non-gso skbs are never this long (like the driver did before) then > we should never clear SG. If we do we risk one of the gso-generated > segs will also be longer than 32 frags. If I read the comment (deleted in this patch), it seems the 32 limits is about TSO only ? #warning Typhoon only supports 32 entries in its SG list for TSO, disabling TSO This is why I chose this implementation. > > Thought I should ask. > > > + } > > + return features; > > return vlan_features_check(skb, features) ? Hmm... not sure why we duplicate vlan_features_check() & vxlan_features_check() in all ndo_features_check() handlers :/ > > > +} > > +#endif > > + > > static const struct net_device_ops typhoon_netdev_ops = { > > .ndo_open = typhoon_open, > > .ndo_stop = typhoon_close, > > +#if MAX_SKB_FRAGS > 32 > > + .ndo_features_check = typhoon_features_check, > > +#endif > > .ndo_start_xmit = typhoon_start_tx, > > .ndo_set_rx_mode = typhoon_set_rx_mode, > > .ndo_tx_timeout = typhoon_tx_timeout, >
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