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    Subject[PATCH 3/7] [I/OAT] Don't offload copies for loopback traffic
    Date
    Local traffic (loopback) is generally in cache anyway, and the overhead
    cost of offloading the copy is worse than just doing it with the CPU.

    Signed-off-by: Chris Leech <christopher.leech@intel.com>
    ---

    net/ipv4/tcp.c | 4 +++-
    1 files changed, 3 insertions(+), 1 deletions(-)

    diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
    index 36f6b64..7971e73 100644
    --- a/net/ipv4/tcp.c
    +++ b/net/ipv4/tcp.c
    @@ -1107,6 +1107,7 @@ int tcp_recvmsg(struct kiocb *iocb, stru
    int copied_early = 0;
    int available = 0;
    struct sk_buff *skb;
    + struct dst_entry *dst;

    lock_sock(sk);

    @@ -1136,7 +1137,8 @@ int tcp_recvmsg(struct kiocb *iocb, stru
    skb = skb_peek_tail(&sk->sk_receive_queue);
    if (skb)
    available = TCP_SKB_CB(skb)->seq + skb->len - (*seq);
    - if ((available < target) &&
    + dst = __sk_dst_get(sk);
    + if ((available < target) && (!dst || (dst->dev != &loopback_dev)) &&
    (len > sysctl_tcp_dma_copybreak) && !(flags & MSG_PEEK) &&
    !sysctl_tcp_low_latency && __get_cpu_var(softnet_data).net_dma) {
    preempt_enable_no_resched();
    -
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