Merge branch 'tcp-do-not-use-tcp_time_stamp-for-rcv-autotuning'

Eric Dumazet says:

====================
tcp: do not use tcp_time_stamp for rcv autotuning

Some devices or linux distributions use HZ=100 or HZ=250

TCP receive buffer autotuning has poor behavior caused by this choice.
Since autotuning happens after 4 ms or 10 ms, short distance flows
get their receive buffer tuned to a very high value, but after an initial
period where it was frozen to (too small) initial value.

With BBR (or other CC allowing to increase BDP), we are willing to
increase tcp_rmem[2], but this receive autotuning defect is a blocker
for hosts dealing with gazillions of TCP flows in the data centers,
since many of them have inflated RCVBUF. Risk of OOM is too high.

Note that TSO autodefer, tcp cubic, and TCP TS options (RFC 7323)
also suffer from our dependency to jiffies (via tcp_time_stamp).

We have ongoing efforts to improve all that in the future.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 6 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index cbe5b602a2d3..b6d5adcee8fc 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -240,6 +240,7 @@ struct tcp_sock {
 	u32	tlp_high_seq;	/* snd_nxt at the time of TLP retransmit. */
 
 /* RTT measurement */
+	struct skb_mstamp tcp_mstamp; /* most recent packet received/sent */
 	u32	srtt_us;	/* smoothed round trip time << 3 in usecs */
 	u32	mdev_us;	/* medium deviation			*/
 	u32	mdev_max_us;	/* maximal mdev for the last rtt period	*/
@@ -332,16 +333,16 @@ struct tcp_sock {
 
 /* Receiver side RTT estimation */
 	struct {
-		u32	rtt;
-		u32	seq;
-		u32	time;
+		u32		rtt_us;
+		u32		seq;
+		struct skb_mstamp time;
 	} rcv_rtt_est;
 
 /* Receiver queue space */
 	struct {
-		int	space;
-		u32	seq;
-		u32	time;
+		int		space;
+		u32		seq;
+		struct skb_mstamp time;
 	} rcvq_space;
 
 /* TCP-specific MTU probe information. */