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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>
Cc: sameehj@amazon.com, netdev@vger.kernel.org, bpf@vger.kernel.org,
	zorik@amazon.com, akiyano@amazon.com, gtzalik@amazon.com,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Daniel Borkmann" <borkmann@iogearbox.net>,
	"Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Alexander Duyck" <alexander.duyck@gmail.com>,
	"Jeff Kirsher" <jeffrey.t.kirsher@intel.com>,
	"David Ahern" <dsahern@gmail.com>,
	"Willem de Bruijn" <willemdebruijn.kernel@gmail.com>,
	"Ilias Apalodimas" <ilias.apalodimas@linaro.org>,
	"Lorenzo Bianconi" <lorenzo@kernel.org>,
	"Saeed Mahameed" <saeedm@mellanox.com>,
	steffen.klassert@secunet.com
Subject: Re: [PATCH net-next v2 21/33] virtio_net: add XDP frame size in two code paths
Date: Fri, 8 May 2020 10:05:46 +0800
Message-ID: <6e86e5de-8558-0f3b-53ce-ab0f611cc649@redhat.com> (raw)
In-Reply-To: <20200506163414-mutt-send-email-mst@kernel.org>


On 2020/5/7 上午4:34, Michael S. Tsirkin wrote:
> On Thu, Apr 30, 2020 at 01:22:08PM +0200, Jesper Dangaard Brouer wrote:
>> The virtio_net driver is running inside the guest-OS. There are two
>> XDP receive code-paths in virtio_net, namely receive_small() and
>> receive_mergeable(). The receive_big() function does not support XDP.
>>
>> In receive_small() the frame size is available in buflen. The buffer
>> backing these frames are allocated in add_recvbuf_small() with same
>> size, except for the headroom, but tailroom have reserved room for
>> skb_shared_info. The headroom is encoded in ctx pointer as a value.
>>
>> In receive_mergeable() the frame size is more dynamic. There are two
>> basic cases: (1) buffer size is based on a exponentially weighted
>> moving average (see DECLARE_EWMA) of packet length. Or (2) in case
>> virtnet_get_headroom() have any headroom then buffer size is
>> PAGE_SIZE. The ctx pointer is this time used for encoding two values;
>> the buffer len "truesize" and headroom. In case (1) if the rx buffer
>> size is underestimated, the packet will have been split over more
>> buffers (num_buf info in virtio_net_hdr_mrg_rxbuf placed in top of
>> buffer area). If that happens the XDP path does a xdp_linearize_page
>> operation.
>>
>> Cc: Jason Wang<jasowang@redhat.com>
>> Signed-off-by: Jesper Dangaard Brouer<brouer@redhat.com>
> Acked-by: Michael S. Tsirkin<mst@redhat.com>


Note that we do:

         xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM + vi->hdr_len;

So using PAGE_SIZE here is probably not correct.

Thanks

>


  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <158824557985.2172139.4173570969543904434.stgit@firesoul>
2020-04-30 11:20 ` [PATCH net-next v2 01/33] xdp: add frame size to xdp_buff Jesper Dangaard Brouer
2020-04-30 11:20 ` [PATCH net-next v2 02/33] bnxt: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-30 11:20 ` [PATCH net-next v2 03/33] sfc: add XDP frame size Jesper Dangaard Brouer
2020-04-30 11:20 ` [PATCH net-next v2 04/33] mvneta: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-30 11:20 ` [PATCH net-next v2 05/33] net: netsec: Add support for XDP frame size Jesper Dangaard Brouer
2020-04-30 11:20 ` [PATCH net-next v2 06/33] net: XDP-generic determining " Jesper Dangaard Brouer
2020-04-30 11:20 ` [PATCH net-next v2 07/33] xdp: xdp_frame add member frame_sz and handle in convert_to_xdp_frame Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 08/33] xdp: cpumap redirect use frame_sz and increase skb_tailroom Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 09/33] veth: adjust hard_start offset on redirect XDP frames Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 10/33] veth: xdp using frame_sz in veth driver Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 11/33] dpaa2-eth: add XDP frame size Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 12/33] hv_netvsc: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-30 14:20   ` Haiyang Zhang
2020-05-01 14:47     ` Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 13/33] qlogic/qede: " Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 14/33] net: ethernet: ti: add XDP frame size to driver cpsw Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 15/33] ena: add XDP frame size to amazon NIC driver Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 16/33] mlx4: add XDP frame size and adjust max XDP MTU Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 17/33] net: thunderx: add XDP frame size Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 18/33] nfp: add XDP frame size to netronome driver Jesper Dangaard Brouer
2020-04-30 11:21 ` [PATCH net-next v2 19/33] tun: add XDP frame size Jesper Dangaard Brouer
2020-05-06 20:32   ` Michael S. Tsirkin
2020-04-30 11:22 ` [PATCH net-next v2 20/33] vhost_net: also populate " Jesper Dangaard Brouer
2020-05-06  6:41   ` Jason Wang
2020-05-06  6:49     ` Jason Wang
2020-05-06 20:33   ` Michael S. Tsirkin
2020-04-30 11:22 ` [PATCH net-next v2 21/33] virtio_net: add XDP frame size in two code paths Jesper Dangaard Brouer
2020-05-06 20:34   ` Michael S. Tsirkin
2020-05-08  2:05     ` Jason Wang [this message]
2020-05-08  7:21       ` Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 22/33] ixgbe: fix XDP redirect on archs with PAGE_SIZE above 4K Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 23/33] ixgbe: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 24/33] ixgbevf: add XDP frame size to VF driver Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 25/33] i40e: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 26/33] ice: " Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 27/33] xdp: for Intel AF_XDP drivers add XDP frame_sz Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 28/33] mlx5: rx queue setup time determine frame_sz for XDP Jesper Dangaard Brouer
2020-04-30 17:07   ` Tariq Toukan
2020-04-30 17:12     ` Tariq Toukan
2020-05-01 12:32       ` Jesper Dangaard Brouer
2020-05-08 10:49         ` Jesper Dangaard Brouer
2020-05-01 13:01     ` Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 29/33] xdp: allow bpf_xdp_adjust_tail() to grow packet size Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 30/33] xdp: clear grow memory in bpf_xdp_adjust_tail() Jesper Dangaard Brouer
2020-04-30 11:22 ` [PATCH net-next v2 31/33] bpf: add xdp.frame_sz in bpf_prog_test_run_xdp() Jesper Dangaard Brouer
2020-04-30 11:23 ` [PATCH net-next v2 32/33] selftests/bpf: adjust BPF selftest for xdp_adjust_tail Jesper Dangaard Brouer
2020-04-30 11:23 ` [PATCH net-next v2 33/33] selftests/bpf: xdp_adjust_tail add grow tail tests Jesper Dangaard Brouer

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