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author | 2017-04-25 10:15:41 -0700 | |
---|---|---|
committer | 2017-04-26 14:44:39 -0400 | |
commit | 645f4c6f2ebd040688cc2a5f626ffc909e66ccf2 (patch) | |
tree | 7ceebdc356adf410a9d78bd51d7e200697d19658 /net/ipv4/tcp_input.c | |
parent | tcp: remove ack_time from struct tcp_sacktag_state (diff) | |
download | linux-645f4c6f2ebd040688cc2a5f626ffc909e66ccf2.tar.gz linux-645f4c6f2ebd040688cc2a5f626ffc909e66ccf2.tar.bz2 linux-645f4c6f2ebd040688cc2a5f626ffc909e66ccf2.zip |
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@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_input.c')
-rw-r--r-- | net/ipv4/tcp_input.c | 28 |
1 files changed, 17 insertions, 11 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index f475f0b53bfe..9739962bfb3f 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 |