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Date: Sun, 10 May 2020 09:31:41 +0300 From: Tariq Toukan <tariqt@...lanox.com> To: Jesper Dangaard Brouer <brouer@...hat.com>, sameehj@...zon.com Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, Toke Høiland-Jørgensen <toke@...hat.com>, Daniel Borkmann <borkmann@...earbox.net>, Alexei Starovoitov <alexei.starovoitov@...il.com>, "David S. Miller" <davem@...emloft.net>, John Fastabend <john.fastabend@...il.com>, Alexander Duyck <alexander.duyck@...il.com>, Jeff Kirsher <jeffrey.t.kirsher@...el.com>, David Ahern <dsahern@...il.com>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, Lorenzo Bianconi <lorenzo@...nel.org>, Saeed Mahameed <saeedm@...lanox.com> Subject: Re: [PATCH net-next v3 28/33] mlx5: rx queue setup time determine frame_sz for XDP On 5/8/2020 2:11 PM, Jesper Dangaard Brouer wrote: > The mlx5 driver have multiple memory models, which are also changed > according to whether a XDP bpf_prog is attached. > > The 'rx_striding_rq' setting is adjusted via ethtool priv-flags e.g.: > # ethtool --set-priv-flags mlx5p2 rx_striding_rq off > > On the general case with 4K page_size and regular MTU packet, then > the frame_sz is 2048 and 4096 when XDP is enabled, in both modes. > > The info on the given frame size is stored differently depending on the > RQ-mode and encoded in a union in struct mlx5e_rq union wqe/mpwqe. > In rx striding mode rq->mpwqe.log_stride_sz is either 11 or 12, which > corresponds to 2048 or 4096 (MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ). > In non-striding mode (MLX5_WQ_TYPE_CYCLIC) the frag_stride is stored > in rq->wqe.info.arr[0].frag_stride, for the first fragment, which is > what the XDP case cares about. > > To reduce effect on fast-path, this patch determine the frame_sz at > setup time, to avoid determining the memory model runtime. Variable > is named first_frame_sz to make it clear that this is only the frame > size of the first fragment. > > This mlx5 driver does a DMA-sync on XDP_TX action, but grow is safe > as it have done a DMA-map on the entire PAGE_SIZE. The driver also > already does a XDP length check against sq->hw_mtu on the possible > XDP xmit paths mlx5e_xmit_xdp_frame() + mlx5e_xmit_xdp_frame_mpwqe(). > > V2: Fix that frag_size need to be recalc before creating SKB. > > Cc: Tariq Toukan <tariqt@...lanox.com> > Cc: Saeed Mahameed <saeedm@...lanox.com> > Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com> > --- Thanks Jesper. Acked-by: Tariq Toukan <tariqt@...lanox.com>
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