Re: [PATCH net-next] tcp: remove loop to compute wscale
From: Soheil Hassas Yeganeh <hidden>
Date: 2018-11-30 03:10:05
On Thu, Nov 29, 2018 at 10:56 AM Eric Dumazet [off-list ref] wrote:
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 <redacted> Very nice, thank you, Eric!
quoted hunk ↗ jump to hunk
--- 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