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    Subject[PATCH 5.4 01/24] net: dsa: add GRO support via gro_cells
    Date
    From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    From: Alexander Lobakin <bloodyreaper@yandex.ru>

    commit e131a5634830047923c694b4ce0c3b31745ff01b upstream.

    gro_cells lib is used by different encapsulating netdevices, such as
    geneve, macsec, vxlan etc. to speed up decapsulated traffic processing.
    CPU tag is a sort of "encapsulation", and we can use the same mechs to
    greatly improve overall DSA performance.
    skbs are passed to the GRO layer after removing CPU tags, so we don't
    need any new packet offload types as it was firstly proposed by me in
    the first GRO-over-DSA variant [1].

    The size of struct gro_cells is sizeof(void *), so hot struct
    dsa_slave_priv becomes only 4/8 bytes bigger, and all critical fields
    remain in one 32-byte cacheline.
    The other positive side effect is that drivers for network devices
    that can be shipped as CPU ports of DSA-driven switches can now use
    napi_gro_frags() to pass skbs to kernel. Packets built that way are
    completely non-linear and are likely being dropped without GRO.

    This was tested on to-be-mainlined-soon Ethernet driver that uses
    napi_gro_frags(), and the overall performance was on par with the
    variant from [1], sometimes even better due to minimal overhead.
    net.core.gro_normal_batch tuning may help to push it to the limit
    on particular setups and platforms.

    iperf3 IPoE VLAN NAT TCP forwarding (port1.218 -> port0) setup
    on 1.2 GHz MIPS board:

    5.7-rc2 baseline:

    [ID] Interval Transfer Bitrate Retr
    [ 5] 0.00-120.01 sec 9.00 GBytes 644 Mbits/sec 413 sender
    [ 5] 0.00-120.00 sec 8.99 GBytes 644 Mbits/sec receiver

    Iface RX packets TX packets
    eth0 7097731 7097702
    port0 426050 6671829
    port1 6671681 425862
    port1.218 6671677 425851

    With this patch:

    [ID] Interval Transfer Bitrate Retr
    [ 5] 0.00-120.01 sec 12.2 GBytes 870 Mbits/sec 122 sender
    [ 5] 0.00-120.00 sec 12.2 GBytes 870 Mbits/sec receiver

    Iface RX packets TX packets
    eth0 9474792 9474777
    port0 455200 353288
    port1 9019592 455035
    port1.218 353144 455024

    v2:
    - Add some performance examples in the commit message;
    - No functional changes.

    [1] https://lore.kernel.org/netdev/20191230143028.27313-1-alobakin@dlink.ru/

    Signed-off-by: Alexander Lobakin <bloodyreaper@yandex.ru>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Cc: Pali Rohár <pali@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/dsa/Kconfig | 1 +
    net/dsa/dsa.c | 2 +-
    net/dsa/dsa_priv.h | 3 +++
    net/dsa/slave.c | 10 +++++++++-
    4 files changed, 14 insertions(+), 2 deletions(-)

    --- a/net/dsa/Kconfig
    +++ b/net/dsa/Kconfig
    @@ -9,6 +9,7 @@ menuconfig NET_DSA
    tristate "Distributed Switch Architecture"
    depends on HAVE_NET_DSA
    depends on BRIDGE || BRIDGE=n
    + select GRO_CELLS
    select NET_SWITCHDEV
    select PHYLINK
    select NET_DEVLINK
    --- a/net/dsa/dsa.c
    +++ b/net/dsa/dsa.c
    @@ -238,7 +238,7 @@ static int dsa_switch_rcv(struct sk_buff
    if (dsa_skb_defer_rx_timestamp(p, skb))
    return 0;

    - netif_receive_skb(skb);
    + gro_cells_receive(&p->gcells, skb);

    return 0;
    }
    --- a/net/dsa/dsa_priv.h
    +++ b/net/dsa/dsa_priv.h
    @@ -11,6 +11,7 @@
    #include <linux/netdevice.h>
    #include <linux/netpoll.h>
    #include <net/dsa.h>
    +#include <net/gro_cells.h>

    enum {
    DSA_NOTIFIER_AGEING_TIME,
    @@ -68,6 +69,8 @@ struct dsa_slave_priv {

    struct pcpu_sw_netstats *stats64;

    + struct gro_cells gcells;
    +
    /* DSA port data, such as switch, port index, etc. */
    struct dsa_port *dp;

    --- a/net/dsa/slave.c
    +++ b/net/dsa/slave.c
    @@ -1431,6 +1431,11 @@ int dsa_slave_create(struct dsa_port *po
    free_netdev(slave_dev);
    return -ENOMEM;
    }
    +
    + ret = gro_cells_init(&p->gcells, slave_dev);
    + if (ret)
    + goto out_free;
    +
    p->dp = port;
    INIT_LIST_HEAD(&p->mall_tc_list);
    INIT_WORK(&port->xmit_work, dsa_port_xmit_work);
    @@ -1443,7 +1448,7 @@ int dsa_slave_create(struct dsa_port *po
    ret = dsa_slave_phy_setup(slave_dev);
    if (ret) {
    netdev_err(master, "error %d setting up slave phy\n", ret);
    - goto out_free;
    + goto out_gcells;
    }

    dsa_slave_notify(slave_dev, DSA_PORT_REGISTER);
    @@ -1462,6 +1467,8 @@ out_phy:
    phylink_disconnect_phy(p->dp->pl);
    rtnl_unlock();
    phylink_destroy(p->dp->pl);
    +out_gcells:
    + gro_cells_destroy(&p->gcells);
    out_free:
    free_percpu(p->stats64);
    free_netdev(slave_dev);
    @@ -1482,6 +1489,7 @@ void dsa_slave_destroy(struct net_device
    dsa_slave_notify(slave_dev, DSA_PORT_UNREGISTER);
    unregister_netdev(slave_dev);
    phylink_destroy(dp->pl);
    + gro_cells_destroy(&p->gcells);
    free_percpu(p->stats64);
    free_netdev(slave_dev);
    }

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