On Thu, Nov 29, 2018 at 10:56 AM Eric Dumazet <eduma...@google.com> wrote:
>
> We can remove the loop and conditional branches
> and compute wscale efficiently thanks to ilog2()
>
> Signed-off-by: Eric Dumazet <eduma...@google.com>
Acked-by: Soheil Hassas Yeganeh <soh...@google.com>
Very nice, thank you, Eric!
> ---
> net/ipv4/tcp_output.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index
> 3ae4a277991a3473f61b1f73acd5ee355cf6a5df..d3b691f3a9e896ce340ae081a0d24092024361c8
> 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -233,16 +233,14 @@ void tcp_select_initial_window(const struct sock *sk,
> int __space, __u32 mss,
> if (init_rcv_wnd)
> *rcv_wnd = min(*rcv_wnd, init_rcv_wnd * mss);
>
> - (*rcv_wscale) = 0;
> + *rcv_wscale = 0;
> if (wscale_ok) {
> /* Set window scaling on max possible window */
> space = max_t(u32, space,
> sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
> space = max_t(u32, space, sysctl_rmem_max);
> space = min_t(u32, space, *window_clamp);
> - while (space > U16_MAX && (*rcv_wscale) < TCP_MAX_WSCALE) {
> - space >>= 1;
> - (*rcv_wscale)++;
> - }
> + *rcv_wscale = clamp_t(int, ilog2(space) - 15,
> + 0, TCP_MAX_WSCALE);
> }
> /* Set the clamp no higher than max representable value */
> (*window_clamp) = min_t(__u32, U16_MAX << (*rcv_wscale),
> *window_clamp);
> --
> 2.20.0.rc0.387.gc7a69e6b6c-goog
>
