Re: [PATCH net-next] net: use ktime_t in struct scm_timestamping_internal

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Eric Dumazet wrote:
> Instead of using struct timespec64 in scm_timestamping_internal,
> use ktime_t, saving 24 bytes in kernel stack.
> 
> This makes tcp_update_recv_tstamps() small enough to be inlined.
> 
> The ktime_t -> timespec64 conversions happen after socket lock
> has been released in tcp_recvmsg(), and only if the application
> requested them.
> 
> $ scripts/bloat-o-meter -t vmlinux.0 vmlinux
> add/remove: 0/2 grow/shrink: 5/4 up/down: 146/-277 (-131)
> Function                                     old     new   delta
> tcp_zerocopy_receive                        2383    2425     +42
> mptcp_recvmsg                               1565    1607     +42
> tcp_recvmsg_locked                          3797    3823     +26
> put_cmsg_scm_timestamping64                  131     149     +18
> put_cmsg_scm_timestamping                    131     149     +18
> __pfx_tcp_update_recv_tstamps                 16       -     -16
> do_tcp_getsockopt                           4024    4006     -18
> tcp_recv_timestamp                           474     430     -44
> tcp_zc_handle_leftover                       417     371     -46
> __sock_recv_timestamp                       1087    1031     -56
> tcp_update_recv_tstamps                       97       -     -97
> Total: Before=25223788, After=25223657, chg -0.00%
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>