tcp: remove loop to compute wscale

We can remove the loop and conditional branches
and compute wscale efficiently thanks to ilog2()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index c5dc4c4fdaddd553e6734d51bd9e3698f6d68e65..e4c1e51b18c1f645286eb837e8aa69011d8de406 100644 (file)
--- 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);