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Date: Mon, 5 Dec 2016 02:54:06 +0200
From: Saeed Mahameed <saeedm@....mellanox.co.il>
To: Martin KaFai Lau <kafai@...com>
Cc: Linux Netdev List <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...com>,
Brenden Blanco <bblanco@...mgrid.com>,
Daniel Borkmann <daniel@...earbox.net>,
David Miller <davem@...emloft.net>,
Jesper Dangaard Brouer <brouer@...hat.com>,
Saeed Mahameed <saeedm@...lanox.com>,
Tariq Toukan <tariqt@...lanox.com>,
Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 net-next 3/4] mlx4: xdp: Reserve headroom for receiving
packet when XDP prog is active
On Sun, Dec 4, 2016 at 5:17 AM, Martin KaFai Lau <kafai@...com> wrote:
> Reserve XDP_PACKET_HEADROOM and honor bpf_xdp_adjust_head()
> when XDP prog is active. This patch only affects the code
> path when XDP is active.
>
> Signed-off-by: Martin KaFai Lau <kafai@...com>
> ---
Hi Martin, Sorry for the late review, i have some comments below
> drivers/net/ethernet/mellanox/mlx4/en_netdev.c | 17 +++++++++++++++--
> drivers/net/ethernet/mellanox/mlx4/en_rx.c | 23 +++++++++++++++++------
> drivers/net/ethernet/mellanox/mlx4/en_tx.c | 9 +++++----
> drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 3 ++-
> 4 files changed, 39 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> index 311c14153b8b..094a13b52cf6 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> @@ -51,7 +51,8 @@
> #include "mlx4_en.h"
> #include "en_port.h"
>
> -#define MLX4_EN_MAX_XDP_MTU ((int)(PAGE_SIZE - ETH_HLEN - (2 * VLAN_HLEN)))
> +#define MLX4_EN_MAX_XDP_MTU ((int)(PAGE_SIZE - ETH_HLEN - (2 * VLAN_HLEN) - \
> + XDP_PACKET_HEADROOM))
>
> int mlx4_en_setup_tc(struct net_device *dev, u8 up)
> {
> @@ -1551,6 +1552,7 @@ int mlx4_en_start_port(struct net_device *dev)
> struct mlx4_en_tx_ring *tx_ring;
> int rx_index = 0;
> int err = 0;
> + int mtu;
> int i, t;
> int j;
> u8 mc_list[16] = {0};
> @@ -1684,8 +1686,12 @@ int mlx4_en_start_port(struct net_device *dev)
> }
>
> /* Configure port */
> + mtu = priv->rx_skb_size + ETH_FCS_LEN;
> + if (priv->tx_ring_num[TX_XDP])
> + mtu += XDP_PACKET_HEADROOM;
> +
Why would the physical MTU care for the headroom you preserve for XDP prog?
This is the wire MTU, it shouldn't be changed, please keep it as
before, any preservation you make in packets buffers are needed only
for FWD case or modify case (HW or wire should not care about them).
> err = mlx4_SET_PORT_general(mdev->dev, priv->port,
> - priv->rx_skb_size + ETH_FCS_LEN,
> + mtu,
> priv->prof->tx_pause,
> priv->prof->tx_ppp,
> priv->prof->rx_pause,
> @@ -2255,6 +2261,13 @@ static bool mlx4_en_check_xdp_mtu(struct net_device *dev, int mtu)
> {
> struct mlx4_en_priv *priv = netdev_priv(dev);
>
> + if (mtu + XDP_PACKET_HEADROOM > priv->max_mtu) {
> + en_err(priv,
> + "Device max mtu:%d does not allow %d bytes reserved headroom for XDP prog\n",
> + priv->max_mtu, XDP_PACKET_HEADROOM);
> + return false;
> + }
> +
> if (mtu > MLX4_EN_MAX_XDP_MTU) {
> en_err(priv, "mtu:%d > max:%d when XDP prog is attached\n",
> mtu, MLX4_EN_MAX_XDP_MTU);
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index 23e9d04d1ef4..324771ac929e 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -96,7 +96,6 @@ static int mlx4_en_alloc_frags(struct mlx4_en_priv *priv,
> struct mlx4_en_rx_alloc page_alloc[MLX4_EN_MAX_RX_FRAGS];
> const struct mlx4_en_frag_info *frag_info;
> struct page *page;
> - dma_addr_t dma;
> int i;
>
> for (i = 0; i < priv->num_frags; i++) {
> @@ -115,9 +114,10 @@ static int mlx4_en_alloc_frags(struct mlx4_en_priv *priv,
>
> for (i = 0; i < priv->num_frags; i++) {
> frags[i] = ring_alloc[i];
> - dma = ring_alloc[i].dma + ring_alloc[i].page_offset;
> + frags[i].page_offset += priv->frag_info[i].rx_headroom;
I don't see any need for headroom on frag_info other that frag0 (which
where the packet starts).
What is the meaning of a headroom of a frag in a middle of a packet ?
if you agree with me then, you can use XDP_PACKET_HEADROOM as is where
needed (i.e frag0 page offset) and remove
"priv->frag_info[i].rx_headroom"
...
After going through the code a little bit i see that this code is
shared between XDP and common path, and you didn't want to add boolean
conditions.
Ok i see what you did here.
Maybe we can pass headroom as a function parameter and split frag0
handling from the rest ?
If it is too much then i am ok with the code as it is,
> + rx_desc->data[i].addr = cpu_to_be64(frags[i].dma +
> + frags[i].page_offset);
> ring_alloc[i] = page_alloc[i];
> - rx_desc->data[i].addr = cpu_to_be64(dma);
> }
>
> return 0;
> @@ -250,7 +250,8 @@ static int mlx4_en_prepare_rx_desc(struct mlx4_en_priv *priv,
>
> if (ring->page_cache.index > 0) {
> frags[0] = ring->page_cache.buf[--ring->page_cache.index];
> - rx_desc->data[0].addr = cpu_to_be64(frags[0].dma);
> + rx_desc->data[0].addr = cpu_to_be64(frags[0].dma +
> + frags[0].page_offset);
> return 0;
> }
>
> @@ -889,6 +890,7 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
> if (xdp_prog) {
> struct xdp_buff xdp;
> dma_addr_t dma;
> + void *pg_addr, *orig_data;
> u32 act;
>
> dma = be64_to_cpu(rx_desc->data[0].addr);
> @@ -896,11 +898,18 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
> priv->frag_info[0].frag_size,
> DMA_FROM_DEVICE);
>
> - xdp.data = page_address(frags[0].page) +
> - frags[0].page_offset;
> + pg_addr = page_address(frags[0].page);
> + orig_data = pg_addr + frags[0].page_offset;
> + xdp.data = orig_data;
> xdp.data_end = xdp.data + length;
>
> act = bpf_prog_run_xdp(xdp_prog, &xdp);
> +
> + if (xdp.data != orig_data) {
> + length = xdp.data_end - xdp.data;
> + frags[0].page_offset = xdp.data - pg_addr;
> + }
> +
>
is this needed only for XDP FWD case ?
is this the only way to detect that the user modified the packet
headers (comparing pointers, before and after) ?
if the answer is yes, it should be faster to unconditionally reset
packet offset and lenght on XDP_FWD :
case XDP_FWD:
length = xdp.data_end - xdp.data;
frags[0].page_offset = xdp.data - pg_addr;
> switch (act) {
> case XDP_PASS:
> break;
> @@ -1180,6 +1189,7 @@ void mlx4_en_calc_rx_buf(struct net_device *dev)
> */
> priv->frag_info[0].frag_stride = PAGE_SIZE;
> priv->frag_info[0].dma_dir = PCI_DMA_BIDIRECTIONAL;
> + priv->frag_info[0].rx_headroom = XDP_PACKET_HEADROOM;
> i = 1;
> } else {
> int buf_size = 0;
> @@ -1194,6 +1204,7 @@ void mlx4_en_calc_rx_buf(struct net_device *dev)
> ALIGN(priv->frag_info[i].frag_size,
> SMP_CACHE_BYTES);
> priv->frag_info[i].dma_dir = PCI_DMA_FROMDEVICE;
> + priv->frag_info[i].rx_headroom = 0;
IMHO, redundant. as you see here frag0 and other frags handling are
separated, maybe we can do the same in mlx4_en_alloc_frags.
> buf_size += priv->frag_info[i].frag_size;
> i++;
> }
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> index 4b597dca5c52..9e5f38cefe5f 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
> @@ -354,7 +354,7 @@ u32 mlx4_en_recycle_tx_desc(struct mlx4_en_priv *priv,
> struct mlx4_en_rx_alloc frame = {
> .page = tx_info->page,
> .dma = tx_info->map0_dma,
> - .page_offset = 0,
> + .page_offset = XDP_PACKET_HEADROOM,
> .page_size = PAGE_SIZE,
> };
>
> @@ -1132,7 +1132,7 @@ netdev_tx_t mlx4_en_xmit_frame(struct mlx4_en_rx_ring *rx_ring,
> tx_info->page = frame->page;
> frame->page = NULL;
> tx_info->map0_dma = dma;
> - tx_info->map0_byte_count = length;
> + tx_info->map0_byte_count = length + frame->page_offset;
Didn't you already take care of lenght by the following code:
if (xdp.data != orig_data) {
length = xdp.data_end - xdp.data;
frags[0].page_offset = xdp.data - pg_addr;
}
and here frame->page_offset is not really page offset, it can only be
XDP_PACKET_HEADROOM.
> tx_info->nr_txbb = nr_txbb;
> tx_info->nr_bytes = max_t(unsigned int, length, ETH_ZLEN);
> tx_info->data_offset = (void *)data - (void *)tx_desc;
> @@ -1141,9 +1141,10 @@ netdev_tx_t mlx4_en_xmit_frame(struct mlx4_en_rx_ring *rx_ring,
> tx_info->linear = 1;
> tx_info->inl = 0;
>
> - dma_sync_single_for_device(priv->ddev, dma, length, PCI_DMA_TODEVICE);
> + dma_sync_single_range_for_device(priv->ddev, dma, frame->page_offset,
> + length, PCI_DMA_TODEVICE);
>
> - data->addr = cpu_to_be64(dma);
> + data->addr = cpu_to_be64(dma + frame->page_offset);
> data->lkey = ring->mr_key;
> dma_wmb();
> data->byte_count = cpu_to_be32(length);
> diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> index 20a936428f4a..ba1c6cd0cc79 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> +++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> @@ -475,7 +475,8 @@ struct mlx4_en_frag_info {
> u16 frag_prefix_size;
> u32 frag_stride;
> enum dma_data_direction dma_dir;
> - int order;
> + u16 order;
> + u16 rx_headroom;
> };
>
> #ifdef CONFIG_MLX4_EN_DCB
> --
> 2.5.1
>
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