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    Subject[PATCH 4.16 46/55] tcp: restore autocorking
    Date
    4.16-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 114f39feab360e6c7b0c4238697f223444d662a1 ]

    When adding rb-tree for TCP retransmit queue, we inadvertently broke
    TCP autocorking.

    tcp_should_autocork() should really check if the rtx queue is not empty.

    Tested:

    Before the fix :
    $ nstat -n;./netperf -H 10.246.7.152 -Cc -- -m 500;nstat | grep AutoCork
    MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.7.152 () port 0 AF_INET
    Recv Send Send Utilization Service Demand
    Socket Socket Message Elapsed Send Recv Send Recv
    Size Size Size Time Throughput local remote local remote
    bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB

    540000 262144 500 10.00 2682.85 2.47 1.59 3.618 2.329
    TcpExtTCPAutoCorking 33 0.0

    // Same test, but forcing TCP_NODELAY
    $ nstat -n;./netperf -H 10.246.7.152 -Cc -- -D -m 500;nstat | grep AutoCork
    MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.7.152 () port 0 AF_INET : nodelay
    Recv Send Send Utilization Service Demand
    Socket Socket Message Elapsed Send Recv Send Recv
    Size Size Size Time Throughput local remote local remote
    bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB

    540000 262144 500 10.00 1408.75 2.44 2.96 6.802 8.259
    TcpExtTCPAutoCorking 1 0.0

    After the fix :
    $ nstat -n;./netperf -H 10.246.7.152 -Cc -- -m 500;nstat | grep AutoCork
    MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.7.152 () port 0 AF_INET
    Recv Send Send Utilization Service Demand
    Socket Socket Message Elapsed Send Recv Send Recv
    Size Size Size Time Throughput local remote local remote
    bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB

    540000 262144 500 10.00 5472.46 2.45 1.43 1.761 1.027
    TcpExtTCPAutoCorking 361293 0.0

    // With TCP_NODELAY option
    $ nstat -n;./netperf -H 10.246.7.152 -Cc -- -D -m 500;nstat | grep AutoCork
    MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.7.152 () port 0 AF_INET : nodelay
    Recv Send Send Utilization Service Demand
    Socket Socket Message Elapsed Send Recv Send Recv
    Size Size Size Time Throughput local remote local remote
    bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB

    540000 262144 500 10.00 5454.96 2.46 1.63 1.775 1.174
    TcpExtTCPAutoCorking 315448 0.0

    Fixes: 75c119afe14f ("tcp: implement rb-tree based retransmit queue")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: Michael Wenig <mwenig@vmware.com>
    Tested-by: Michael Wenig <mwenig@vmware.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Reported-by: Michael Wenig <mwenig@vmware.com>
    Tested-by: Michael Wenig <mwenig@vmware.com>
    Acked-by: Neal Cardwell <ncardwell@google.com>
    Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv4/tcp.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/net/ipv4/tcp.c
    +++ b/net/ipv4/tcp.c
    @@ -688,7 +688,7 @@ static bool tcp_should_autocork(struct s
    {
    return skb->len < size_goal &&
    sock_net(sk)->ipv4.sysctl_tcp_autocorking &&
    - skb != tcp_write_queue_head(sk) &&
    + !tcp_rtx_queue_empty(sk) &&
    refcount_read(&sk->sk_wmem_alloc) > skb->truesize;
    }


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