From 19bf62613a800ef4ffa26cbae6b723d9f46740ed Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 29 Nov 2018 07:56:20 -0800
Subject: [PATCH] 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>
---
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 c5dc4c4fdaddd..e4c1e51b18c1f 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);
--
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