On Tue, Jun 29, 2021 at 12:50:53PM +0300, Maxim Mikityanskiy wrote:
> On 2021-06-28 13:47, Maciej Fijalkowski wrote:
> > On Thu, Jun 17, 2021 at 10:55:34PM +0800, Xuan Zhuo wrote:
> > > When each driver supports xsk rx, if the received buff returns XDP_PASS
> > > after run xdp prog, it must construct skb based on xdp. This patch
> > > extracts this logic into a public function xdp_construct_skb().
> > >
> > > There is a bug in the original logic. When constructing skb, we should
> > > copy the meta information to skb and then use __skb_pull() to correct
> > > the data.
> >
> > Thanks for fixing the bug on Intel drivers, Xuan. However, together with
> > Magnus we feel that include/net/xdp.h is not a correct place for
> > introducing xdp_construct_skb. If mlx side could use it, then probably
> > include/net/xdp_sock_drv.h is a better fit for that.
> >
> > Once again, CCing Maxim.
> > Maxim, any chances that mlx driver could be aligned in a way that we could
> > have a common function for creating skb on ZC path?
>
> I'm sorry I missed the v1.
>
> I have reviewed the differences between mlx5e_xsk_construct_skb and
> xdp_construct_skb. I would say it is possible for mlx5 to adapt and use the
> new API, but it may also require changes to xdp_construct_skb. Please see
> the list of differences below.
Great!
>
> >
> > Otherwise, maybe we should think about introducing the Intel-specific
> > common header in tree?
>
> Sure, you can do it to share Intel-specific stuff between Intel drivers.
> However, in this particular case I think all XSK-enabled drivers would
> benefit from this function, especially after previous efforts that aimed to
> minimize the differences between drivers, the amount of code in the drivers
> and to share as much as possible. So, in my opinion, this stuff belongs to
> xdp_sock_drv.h. (Moreover, I see this patch also changes stmmac, so it's no
> longer Intel-specific.)
Right, stmmac just looked similar to what Intel is doing and AFAICT the
author of that code was from Intel, sorry for assumption.
>
> Differences between mlx5e_xsk_construct_skb and xdp_construct_skb:
>
> 1. __napi_alloc_skb is called with __GFP_NOWARN in xdp_construct_skb, but
> without this flag in mlx5. Why do we need to use non-default flags? Why
> can't we stick with napi_alloc_skb? I see only Intel drivers and XSK in
> stmmac use __napi_alloc_skb instead of napi_alloc_skb, and it looks to me as
> it was just copied from the regular (non-XSK) datapath of i40e
> (i40e_construct_skb) to i40e's XSK, then to stmmac, then to
> xdp_construct_skb, and I don't truly understand the reason of having
> __GFP_NOWARN where it first appeared (i40e_construct_skb). Could someone
> explain the reason for __GFP_NOWARN, so that we could decide whether we want
> it in a generic XSK helper?
It's a c&p to me.
>
> 2. skb_put in mlx5 vs __skb_put in xdp_construct_skb - shouldn't be a big
> deal, the difference is just an extra overflow check in skb_put.
>
> 3. XDP metadata. mlx5 calls xdp_set_data_meta_invalid, while other
> XSK-enabled drivers set metadata size to 0 and allow the XDP program to push
> some metadata. xdp_construct_skb only supports xdp_buffs with metadata, it
> will break if xdp_data_meta_unsupported. There are a few possible ways to
> address it:
>
> 3.1. Add a check for xdp_data_meta_unsupported to xdp_construct_skb. It will
> lift the undocumented limitation of this function and allow it to handle all
> valid kinds of xdp_buff.
>
> 3.2. Have two versions of xdp_construct_skb: one for xdp_buffs with
> metadata, the other for ones without metadata. Sounds ugly and not robust,
> but could spare a few CPU cycles for drivers that can't have metadata.
>
> 3.3. Remove xdp_set_data_meta_invalid from mlx5. I think the reason for this
> call was some design decision, rather than a technical limitation. On the
> other hand, even though it will allow mlx5 to work with xdp_construct_skb in
> its current implementation, it would still be nice to combine it with 3.1 to
> avoid having issues with future drivers (if not, at least document in a
> clear way that the xdp_buff parameter must have metadata). Tariq/Saeed,
> could you comment on this point?
So this sounds like we need to hear from you guys if you're going to add a
support to metadata in AF_XDP ZC. Then we can decide with steps forward.
Thanks for this breakdown!
>
> Thanks,
> Max
>
> > >
> > > Fixes: 0a714186d3c0f ("i40e: add AF_XDP zero-copy Rx support")
> > > Fixes: 2d4238f556972 ("ice: Add support for AF_XDP")
> > > Fixes: bba2556efad66 ("net: stmmac: Enable RX via AF_XDP zero-copy")
> > > Fixes: d0bcacd0a1309 ("ixgbe: add AF_XDP zero-copy Rx support")
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > > ---
> > > drivers/net/ethernet/intel/i40e/i40e_xsk.c | 16 +---------
> > > drivers/net/ethernet/intel/ice/ice_xsk.c | 12 +-------
> > > drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 12 +-------
> > > .../net/ethernet/stmicro/stmmac/stmmac_main.c | 23 +-------------
> > > include/net/xdp.h | 30 +++++++++++++++++++
> > > 5 files changed, 34 insertions(+), 59 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > > index 68f177a86403..81b0f44eedda 100644
> > > --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > > +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > > @@ -246,23 +246,9 @@ bool i40e_alloc_rx_buffers_zc(struct i40e_ring *rx_ring, u16 count)
> > > static struct sk_buff *i40e_construct_skb_zc(struct i40e_ring *rx_ring,
> > > struct xdp_buff *xdp)
> > > {
> > > - unsigned int metasize = xdp->data - xdp->data_meta;
> > > - unsigned int datasize = xdp->data_end - xdp->data;
> > > struct sk_buff *skb;
> > > - /* allocate a skb to store the frags */
> > > - skb = __napi_alloc_skb(&rx_ring->q_vector->napi,
> > > - xdp->data_end - xdp->data_hard_start,
> > > - GFP_ATOMIC | __GFP_NOWARN);
> > > - if (unlikely(!skb))
> > > - goto out;
> > > -
> > > - skb_reserve(skb, xdp->data - xdp->data_hard_start);
> > > - memcpy(__skb_put(skb, datasize), xdp->data, datasize);
> > > - if (metasize)
> > > - skb_metadata_set(skb, metasize);
> > > -
> > > -out:
> > > + skb = xdp_construct_skb(xdp, &rx_ring->q_vector->napi);
> > > xsk_buff_free(xdp);
> > > return skb;
> > > }
> > > diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> > > index a1f89ea3c2bd..f95e1adcebda 100644
> > > --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> > > +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> > > @@ -430,22 +430,12 @@ static void ice_bump_ntc(struct ice_ring *rx_ring)
> > > static struct sk_buff *
> > > ice_construct_skb_zc(struct ice_ring *rx_ring, struct ice_rx_buf *rx_buf)
> > > {
> > > - unsigned int metasize = rx_buf->xdp->data - rx_buf->xdp->data_meta;
> > > - unsigned int datasize = rx_buf->xdp->data_end - rx_buf->xdp->data;
> > > - unsigned int datasize_hard = rx_buf->xdp->data_end -
> > > - rx_buf->xdp->data_hard_start;
> > > struct sk_buff *skb;
> > > - skb = __napi_alloc_skb(&rx_ring->q_vector->napi, datasize_hard,
> > > - GFP_ATOMIC | __GFP_NOWARN);
> > > + skb = xdp_construct_skb(rx_buf->xdp, &rx_ring->q_vector->napi);
> > > if (unlikely(!skb))
> > > return NULL;
> > > - skb_reserve(skb, rx_buf->xdp->data - rx_buf->xdp->data_hard_start);
> > > - memcpy(__skb_put(skb, datasize), rx_buf->xdp->data, datasize);
> > > - if (metasize)
> > > - skb_metadata_set(skb, metasize);
> > > -
> > > xsk_buff_free(rx_buf->xdp);
> > > rx_buf->xdp = NULL;
> > > return skb;
> > > diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> > > index f72d2978263b..123945832c96 100644
> > > --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> > > +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> > > @@ -203,22 +203,12 @@ bool ixgbe_alloc_rx_buffers_zc(struct ixgbe_ring *rx_ring, u16 count)
> > > static struct sk_buff *ixgbe_construct_skb_zc(struct ixgbe_ring *rx_ring,
> > > struct ixgbe_rx_buffer *bi)
> > > {
> > > - unsigned int metasize = bi->xdp->data - bi->xdp->data_meta;
> > > - unsigned int datasize = bi->xdp->data_end - bi->xdp->data;
> > > struct sk_buff *skb;
> > > - /* allocate a skb to store the frags */
> > > - skb = __napi_alloc_skb(&rx_ring->q_vector->napi,
> > > - bi->xdp->data_end - bi->xdp->data_hard_start,
> > > - GFP_ATOMIC | __GFP_NOWARN);
> > > + skb = xdp_construct_skb(bi->xdp, &rx_ring->q_vector->napi);
> > > if (unlikely(!skb))
> > > return NULL;
> > > - skb_reserve(skb, bi->xdp->data - bi->xdp->data_hard_start);
> > > - memcpy(__skb_put(skb, datasize), bi->xdp->data, datasize);
> > > - if (metasize)
> > > - skb_metadata_set(skb, metasize);
> > > -
> > > xsk_buff_free(bi->xdp);
> > > bi->xdp = NULL;
> > > return skb;
> > > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > > index c87202cbd3d6..143ac1edb876 100644
> > > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > > @@ -4729,27 +4729,6 @@ static void stmmac_finalize_xdp_rx(struct stmmac_priv *priv,
> > > xdp_do_flush();
> > > }
> > > -static struct sk_buff *stmmac_construct_skb_zc(struct stmmac_channel *ch,
> > > - struct xdp_buff *xdp)
> > > -{
> > > - unsigned int metasize = xdp->data - xdp->data_meta;
> > > - unsigned int datasize = xdp->data_end - xdp->data;
> > > - struct sk_buff *skb;
> > > -
> > > - skb = __napi_alloc_skb(&ch->rxtx_napi,
> > > - xdp->data_end - xdp->data_hard_start,
> > > - GFP_ATOMIC | __GFP_NOWARN);
> > > - if (unlikely(!skb))
> > > - return NULL;
> > > -
> > > - skb_reserve(skb, xdp->data - xdp->data_hard_start);
> > > - memcpy(__skb_put(skb, datasize), xdp->data, datasize);
> > > - if (metasize)
> > > - skb_metadata_set(skb, metasize);
> > > -
> > > - return skb;
> > > -}
> > > -
> > > static void stmmac_dispatch_skb_zc(struct stmmac_priv *priv, u32 queue,
> > > struct dma_desc *p, struct dma_desc *np,
> > > struct xdp_buff *xdp)
> > > @@ -4761,7 +4740,7 @@ static void stmmac_dispatch_skb_zc(struct stmmac_priv *priv, u32 queue,
> > > struct sk_buff *skb;
> > > u32 hash;
> > > - skb = stmmac_construct_skb_zc(ch, xdp);
> > > + skb = xdp_construct_skb(xdp, &ch->rxtx_napi);
> > > if (!skb) {
> > > priv->dev->stats.rx_dropped++;
> > > return;
> > > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > > index a5bc214a49d9..561e21eaf718 100644
> > > --- a/include/net/xdp.h
> > > +++ b/include/net/xdp.h
> > > @@ -95,6 +95,36 @@ xdp_prepare_buff(struct xdp_buff *xdp, unsigned char *hard_start,
> > > xdp->data_meta = meta_valid ? data : data + 1;
> > > }
> > > +static __always_inline struct sk_buff *
> > > +xdp_construct_skb(struct xdp_buff *xdp, struct napi_struct *napi)
> > > +{
> > > + unsigned int metasize;
> > > + unsigned int datasize;
> > > + unsigned int headroom;
> > > + struct sk_buff *skb;
> > > + unsigned int len;
> > > +
> > > + /* this include metasize */
> > > + datasize = xdp->data_end - xdp->data_meta;
> > > + metasize = xdp->data - xdp->data_meta;
> > > + headroom = xdp->data_meta - xdp->data_hard_start;
> > > + len = xdp->data_end - xdp->data_hard_start;
> > > +
> > > + /* allocate a skb to store the frags */
> > > + skb = __napi_alloc_skb(napi, len, GFP_ATOMIC | __GFP_NOWARN);
> > > + if (unlikely(!skb))
> > > + return NULL;
> > > +
> > > + skb_reserve(skb, headroom);
> > > + memcpy(__skb_put(skb, datasize), xdp->data_meta, datasize);
> > > + if (metasize) {
> > > + __skb_pull(skb, metasize);
> > > + skb_metadata_set(skb, metasize);
> > > + }
> > > +
> > > + return skb;
> > > +}
> > > +
> > > /* Reserve memory area at end-of data area.
> > > *
> > > * This macro reserves tailroom in the XDP buffer by limiting the
> > > --
> > > 2.31.0
> > >
>
