[TCP]: Add two new spurious RTO responses to FRTO

New sysctl tcp_frto_response is added to select amongst these
responses:
	- Rate halving based; reuses CA_CWR state (default)
	- Very conservative; used to be the only one available (=1)
	- Undo cwr; undoes ssthresh and cwnd reductions (=2)

The response with rate halving requires a new parameter to
tcp_enter_cwr because FRTO has already reduced ssthresh and
doing a second reduction there has to be prevented. In addition,
to keep things nice on 80 cols screen, a local variable was
added.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 3 insertions, 1 deletions

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 98e0fd241a25..c9ccb550206f 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -439,6 +439,7 @@ enum
         NET_TCP_AVAIL_CONG_CONTROL=122,
         NET_TCP_ALLOWED_CONG_CONTROL=123,
         NET_TCP_MAX_SSTHRESH=124,
+        NET_TCP_FRTO_RESPONSE=125,
 };
 
 enum {
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6d09f5085f6a..f0c9e3400a09 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -220,6 +220,7 @@ extern int sysctl_tcp_app_win;
 extern int sysctl_tcp_adv_win_scale;
 extern int sysctl_tcp_tw_reuse;
 extern int sysctl_tcp_frto;
+extern int sysctl_tcp_frto_response;
 extern int sysctl_tcp_low_latency;
 extern int sysctl_tcp_dma_copybreak;
 extern int sysctl_tcp_nometrics_save;
@@ -738,7 +739,7 @@ static inline void tcp_sync_left_out(struct tcp_sock *tp)
         tp->left_out = tp->sacked_out + tp->lost_out;
 }
 
-extern void tcp_enter_cwr(struct sock *sk);
+extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);
 extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst);
 
 /* Slow start with delack produces 3 packets of burst, so that