On 04/04/2018 05:30 AM, Paolo Abeni wrote: > After commit 694aba690de0 ("ipv4: factorize sk_wmem_alloc updates > done by __ip_append_data()") and commit 1f4c6eb24029 ("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: 694aba690de0 ("ipv4: factorize sk_wmem_alloc updates done by > __ip_append_data()") > Fixes: 1f4c6eb24029 ("ipv6: factorize sk_wmem_alloc updates done by > __ip6_append_data()") > Signed-off-by: Paolo Abeni <pab...@redhat.com> > ---
SGTM, thanks Paolo Reviewed-by: Eric Dumazet <eduma...@google.com> My intent was to modify sock_alloc_send_pskb() to accept to opt-out the skb_set_owner_w() call, but I forgot that the merge window was starting last week-end. So if a UDP datagram needs 2 skb, only one sk_wmem_alloc change would happen, not 1 + 1.