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Date: Tue, 25 Apr 2017 10:15:41 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>,
Soheil Hassas Yeganeh <soheil@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH net-next 10/10] tcp: switch rcv_rtt_est and rcvq_space to high resolution timestamps
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@...gle.com>
Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
---
include/linux/tcp.h | 12 ++++++------
net/ipv4/tcp.c | 2 +-
net/ipv4/tcp_input.c | 28 +++++++++++++++++-----------
3 files changed, 24 insertions(+), 18 deletions(-)
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
--
2.13.0.rc0.306.g87b477812d-goog
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