On Thu, 30 Apr 2020 20:07:43 +0300 Tariq Toukan <tariqt@xxxxxxxxxxxx> wrote: > On 4/30/2020 2:22 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@xxxxxxxxxxxx> > > Cc: Saeed Mahameed <saeedm@xxxxxxxxxxxx> > > Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> > > --- > > drivers/net/ethernet/mellanox/mlx5/core/en.h | 1 + > > drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c | 1 + > > drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 6 ++++++ > > drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 2 ++ > > 4 files changed, 10 insertions(+) > > [... cut ...] > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > > index e2beb89c1832..04671ed977a5 100644 > > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > > @@ -1084,6 +1084,7 @@ mlx5e_skb_from_cqe_linear(struct mlx5e_rq *rq, struct mlx5_cqe64 *cqe, > > if (consumed) > > return NULL; /* page/packet was consumed by XDP */ > > > > + frag_size = MLX5_SKB_FRAG_SZ(rx_headroom + cqe_bcnt); > > This is a re-calculation of frag_size, using the exact same command used > earlier in this function, but with a newer value of rx_headroom. > This wasn't part of the previous patchset. I understand the need. Yes, kernel will crash without this change. > However, this code repetition looks weird and non-optimal to me. I think > we can come up with something better. > > > skb = mlx5e_build_linear_skb(rq, va, frag_size, rx_headroom, cqe_bcnt); > > if (unlikely(!skb)) > > return NULL; > > @@ -1385,6 +1386,7 @@ mlx5e_skb_from_cqe_mpwrq_linear(struct mlx5e_rq *rq, struct mlx5e_mpw_info *wi, > > return NULL; /* page/packet was consumed by XDP */ > > } > > > > + frag_size = MLX5_SKB_FRAG_SZ(rx_headroom + cqe_bcnt32); > > Same here. > > > skb = mlx5e_build_linear_skb(rq, va, frag_size, rx_headroom, cqe_bcnt32); > > if (unlikely(!skb)) > > return NULL; > > > > > > My suggetion is: > Pass &frag_size to mlx5e_xdp_handle(), and update it within it, just > next to the update of rx_headroom. > All the needed information is there: the new rx_headroom, and cqe_bcnt. First of all, passing yet-another argument to mlx5e_xdp_handle(), also looks weird, and is on the brink of becoming a performance issue, as on x86_64 you can pass max 6 arguments in registers before they get pushed on the stack. Adding this would be the 7th argument. Second the MLX5_SKB_FRAG_SZ() calculation is also weird, because it does not provide any tailroom in the packet, I guess it is for supporting another memory mode, as in case XDP is activated there are plenty of tailroom. I though about increasing the frag_size, but I choose not to, because then this patch would change the driver behavior beyond adding frame_sz for XDP. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer bool mlx5e_xdp_handle(struct mlx5e_rq *rq, struct mlx5e_dma_info *di, void *va, u16 *rx_headroom, u32 *len, bool xsk) { [...] }
