diff mbox

[net-next,10/10] tcp: switch rcv_rtt_est and rcvq_space to high resolution timestamps

Message ID 20170425171541.3417-11-edumazet@google.com
State Accepted, archived
Delegated to: David Miller
Headers show

Commit Message

Eric Dumazet April 25, 2017, 5:15 p.m. UTC 
Some devices or 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 tp->tcp_mstamp introduction, we can switch to high resolution
timestamps almost for free (at the expense of 8 additional bytes per
TCP structure)

Note that some TCP stacks use usec TCP timestamps where this
patch makes even more sense : Many TCP flows have < 500 usec RTT.
Hopefully this finer TS option can be standardized soon.

Tested:
 HZ=100 kernel
 ./netperf -H lpaa24 -t TCP_RR -l 1000 -- -r 10000,10000 &

 Peer without patch :
 lpaa24:~# ss -tmi dst lpaa23
 ...
 skmem:(r0,rb8388608,...)
 rcv_rtt:10 rcv_space:3210000 minrtt:0.017

 Peer with the patch :
 lpaa23:~# ss -tmi dst lpaa24
 ...
 skmem:(r0,rb428800,...)
 rcv_rtt:0.069 rcv_space:30000 minrtt:0.017

We can see saner RCVBUF, and more precise rcv_rtt information.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
---
 include/linux/tcp.h  | 12 ++++++------
 net/ipv4/tcp.c       |  2 +-
 net/ipv4/tcp_input.c | 28 +++++++++++++++++-----------
 3 files changed, 24 insertions(+), 18 deletions(-)

Comments

Neal Cardwell April 25, 2017, 5:54 p.m. UTC | #1 
On Tue, Apr 25, 2017 at 1:15 PM, Eric Dumazet <edumazet@google.com> wrote:
> Some devices or 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 tp->tcp_mstamp introduction, we can switch to high resolution
> timestamps almost for free (at the expense of 8 additional bytes per
> TCP structure)
>
> Note that some TCP stacks use usec TCP timestamps where this
> patch makes even more sense : Many TCP flows have < 500 usec RTT.
> Hopefully this finer TS option can be standardized soon.
>
> Tested:
>  HZ=100 kernel
>  ./netperf -H lpaa24 -t TCP_RR -l 1000 -- -r 10000,10000 &
>
>  Peer without patch :
>  lpaa24:~# ss -tmi dst lpaa23
>  ...
>  skmem:(r0,rb8388608,...)
>  rcv_rtt:10 rcv_space:3210000 minrtt:0.017
>
>  Peer with the patch :
>  lpaa23:~# ss -tmi dst lpaa24
>  ...
>  skmem:(r0,rb428800,...)
>  rcv_rtt:0.069 rcv_space:30000 minrtt:0.017
>
> We can see saner RCVBUF, and more precise rcv_rtt information.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Acked-by: Soheil Hassas Yeganeh <soheil@google.com>

Acked-by: Neal Cardwell <ncardwell@google.com>

neal
diff mbox

Patch

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 99a22f44c32e1587a6bf4835b65c7a4314807aa8..b6d5adcee8fcb611de202993623cc80274d262e4 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -333,16 +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. */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index efc976ae66ae5b82d496323634c3030fb71c6c92..059dad7deefe883bd3a26c93f27637dc22ccefda 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2853,7 +2853,7 @@  void tcp_get_info(struct sock *sk, struct tcp_info *info)
 	info->tcpi_snd_ssthresh = tp->snd_ssthresh;
 	info->tcpi_advmss = tp->advmss;
 
-	info->tcpi_rcv_rtt = jiffies_to_usecs(tp->rcv_rtt_est.rtt)>>3;
+	info->tcpi_rcv_rtt = tp->rcv_rtt_est.rtt_us >> 3;
 	info->tcpi_rcv_space = tp->rcvq_space.space;
 
 	info->tcpi_total_retrans = tp->total_retrans;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f475f0b53bfe4cb67c19b7f30d9d68bd703ff23b..9739962bfb3fd2d39cb13f643def223f4f17fcb6 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -442,7 +442,8 @@  void tcp_init_buffer_space(struct sock *sk)
 		tcp_sndbuf_expand(sk);
 
 	tp->rcvq_space.space = tp->rcv_wnd;
-	tp->rcvq_space.time = tcp_time_stamp;
+	skb_mstamp_get(&tp->tcp_mstamp);
+	tp->rcvq_space.time = tp->tcp_mstamp;
 	tp->rcvq_space.seq = tp->copied_seq;
 
 	maxwin = tcp_full_space(sk);
@@ -518,7 +519,7 @@  EXPORT_SYMBOL(tcp_initialize_rcv_mss);
  */
 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 {
-	u32 new_sample = tp->rcv_rtt_est.rtt;
+	u32 new_sample = tp->rcv_rtt_est.rtt_us;
 	long m = sample;
 
 	if (m == 0)
@@ -548,21 +549,23 @@  static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
 		new_sample = m << 3;
 	}
 
-	if (tp->rcv_rtt_est.rtt != new_sample)
-		tp->rcv_rtt_est.rtt = new_sample;
+	tp->rcv_rtt_est.rtt_us = new_sample;
 }
 
 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
 {
-	if (tp->rcv_rtt_est.time == 0)
+	u32 delta_us;
+
+	if (tp->rcv_rtt_est.time.v64 == 0)
 		goto new_measure;
 	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
 		return;
-	tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rcv_rtt_est.time, 1);
+	delta_us = skb_mstamp_us_delta(&tp->tcp_mstamp, &tp->rcv_rtt_est.time);
+	tcp_rcv_rtt_update(tp, delta_us, 1);
 
 new_measure:
 	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
-	tp->rcv_rtt_est.time = tcp_time_stamp;
+	tp->rcv_rtt_est.time = tp->tcp_mstamp;
 }
 
 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
@@ -572,7 +575,10 @@  static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
 	if (tp->rx_opt.rcv_tsecr &&
 	    (TCP_SKB_CB(skb)->end_seq -
 	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
-		tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
+		tcp_rcv_rtt_update(tp,
+				   jiffies_to_usecs(tcp_time_stamp -
+						    tp->rx_opt.rcv_tsecr),
+				   0);
 }
 
 /*
@@ -585,8 +591,8 @@  void tcp_rcv_space_adjust(struct sock *sk)
 	int time;
 	int copied;
 
-	time = tcp_time_stamp - tp->rcvq_space.time;
-	if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
+	time = skb_mstamp_us_delta(&tp->tcp_mstamp, &tp->rcvq_space.time);
+	if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
 		return;
 
 	/* Number of bytes copied to user in last RTT */
@@ -642,7 +648,7 @@  void tcp_rcv_space_adjust(struct sock *sk)
 
 new_measure:
 	tp->rcvq_space.seq = tp->copied_seq;
-	tp->rcvq_space.time = tcp_time_stamp;
+	tp->rcvq_space.time = tp->tcp_mstamp;
 }
 
 /* There is something which you must keep in mind when you analyze the