• Paolo Abeni's avatar
    net: avoid unneeded atomic operation in ip*_append_data() · 9e8445a5
    Paolo Abeni authored
    After commit 694aba69 ("ipv4: factorize sk_wmem_alloc updates
    done by __ip_append_data()") and commit 1f4c6eb2 ("ipv6:
    factorize sk_wmem_alloc updates done by __ip6_append_data()"),
    when transmitting sub MTU datagram, an addtional, unneeded atomic
    operation is performed in ip*_append_data() to update wmem_alloc:
    in the above condition the delta is 0.
    
    The above cause small but measurable performance regression in UDP
    xmit tput test with packet size below MTU.
    
    This change avoids such overhead updating wmem_alloc only if
    wmem_alloc_delta is non zero.
    
    The error path is left intentionally unmodified: it's a slow path
    and simplicity is preferred to performances.
    
    Fixes: 694aba69 ("ipv4: factorize sk_wmem_alloc updates done by __ip_append_data()")
    Fixes: 1f4c6eb2 ("ipv6: factorize sk_wmem_alloc updates done by __ip6_append_data()")
    Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
    Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9e8445a5
ip6_output.c 45.2 KB