On Thu, Sep 4, 2025 at 4:30 PM Amery Hung <ameryhung@xxxxxxxxx> wrote:
>
> On Thu, Sep 4, 2025 at 3:57 PM Christoph Paasch via B4 Relay
> <devnull+cpaasch.openai.com@xxxxxxxxxx> wrote:
> >
> > From: Christoph Paasch <cpaasch@xxxxxxxxxx>
> >
> > mlx5e_skb_from_cqe_mpwrq_nonlinear() copies MLX5E_RX_MAX_HEAD (256)
> > bytes from the page-pool to the skb's linear part. Those 256 bytes
> > include part of the payload.
> >
> > When attempting to do GRO in skb_gro_receive, if headlen > data_offset
> > (and skb->head_frag is not set), we end up aggregating packets in the
> > frag_list.
> >
> > This is of course not good when we are CPU-limited. Also causes a worse
> > skb->len/truesize ratio,...
> >
> > So, let's avoid copying parts of the payload to the linear part. We use
> > eth_get_headlen() to parse the headers and compute the length of the
> > protocol headers, which will be used to copy the relevant bits ot the
> > skb's linear part.
> >
> > We still allocate MLX5E_RX_MAX_HEAD for the skb so that if the networking
> > stack needs to call pskb_may_pull() later on, we don't need to reallocate
> > memory.
> >
> > This gives a nice throughput increase (ARM Neoverse-V2 with CX-7 NIC and
> > LRO enabled):
> >
> > BEFORE:
> > =======
> > (netserver pinned to core receiving interrupts)
> > $ netperf -H 10.221.81.118 -T 80,9 -P 0 -l 60 -- -m 256K -M 256K
> > 87380 16384 262144 60.01 32547.82
> >
> > (netserver pinned to adjacent core receiving interrupts)
> > $ netperf -H 10.221.81.118 -T 80,10 -P 0 -l 60 -- -m 256K -M 256K
> > 87380 16384 262144 60.00 52531.67
> >
> > AFTER:
> > ======
> > (netserver pinned to core receiving interrupts)
> > $ netperf -H 10.221.81.118 -T 80,9 -P 0 -l 60 -- -m 256K -M 256K
> > 87380 16384 262144 60.00 52896.06
> >
> > (netserver pinned to adjacent core receiving interrupts)
> > $ netperf -H 10.221.81.118 -T 80,10 -P 0 -l 60 -- -m 256K -M 256K
> > 87380 16384 262144 60.00 85094.90
> >
> > Additional tests across a larger range of parameters w/ and w/o LRO, w/
> > and w/o IPv6-encapsulation, different MTUs (1500, 4096, 9000), different
> > TCP read/write-sizes as well as UDP benchmarks, all have shown equal or
> > better performance with this patch.
> >
> > Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> > Reviewed-by: Saeed Mahameed <saeedm@xxxxxxxxxx>
> > Signed-off-by: Christoph Paasch <cpaasch@xxxxxxxxxx>
> > ---
> > drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > index 8bedbda522808cbabc8e62ae91a8c25d66725ebb..0ac31c7fb64cd60720d390de45a5b6b453ed0a3f 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > @@ -2047,6 +2047,8 @@ mlx5e_skb_from_cqe_mpwrq_nonlinear(struct mlx5e_rq *rq, struct mlx5e_mpw_info *w
> > dma_sync_single_for_cpu(rq->pdev, addr + head_offset, headlen,
> > rq->buff.map_dir);
> >
> > + headlen = eth_get_headlen(rq->netdev, head_addr, headlen);
> > +
> > frag_offset += headlen;
> > byte_cnt -= headlen;
> > linear_hr = skb_headroom(skb);
> > @@ -2123,6 +2125,9 @@ mlx5e_skb_from_cqe_mpwrq_nonlinear(struct mlx5e_rq *rq, struct mlx5e_mpw_info *w
> > pagep->frags++;
> > while (++pagep < frag_page);
> > }
> > +
> > + headlen = eth_get_headlen(rq->netdev, mxbuf->xdp.data, headlen);
> > +
>
> The size of mxbuf->xdp.data is most likely not headlen here.
>
> The driver currently generates a xdp_buff with empty linear data, pass
> it to the xdp program and assumes the layout If the xdp program does
> not change the layout of the xdp_buff through bpf_xdp_adjust_head() or
> bpf_xdp_adjust_tail(). The assumption is not correct and I am working
> on a fix. But, if we keep that assumption for now, mxbuf->xdp.data
> will not contain any headers or payload. The thing that you try to do
> probably should be:
>
> skb_frag_t *frag = &sinfo->frags[0];
>
> headlen = eth_get_headlen(rq->netdev, skb_frag_address(frag),
> skb_frag_size(frag));
Ok, I think I understand what you mean! Thanks for taking the time to explain!
I will do some tests on my side to make sure I get it right.
As your change goes to net and mine to netnext, I can wait until yours
is in the tree so that there aren't any conflicts that need to be
taken care of.
Christoph
>
>
>
> > __pskb_pull_tail(skb, headlen);
> > } else {
> > if (xdp_buff_has_frags(&mxbuf->xdp)) {
> >
> > --
> > 2.50.1
> >
> >
