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authorEric Dumazet <edumazet@google.com>2017-04-25 20:15:41 +0300
committerDavid S. Miller <davem@davemloft.net>2017-04-26 21:44:39 +0300
commit645f4c6f2ebd040688cc2a5f626ffc909e66ccf2 (patch)
tree7ceebdc356adf410a9d78bd51d7e200697d19658 /include/linux/tcp.h
parenta6db50b81e3f20b2b692bbddd35d9484057eae9d (diff)
downloadlinux-645f4c6f2ebd040688cc2a5f626ffc909e66ccf2.tar.xz
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 'include/linux/tcp.h')
-rw-r--r--include/linux/tcp.h12
1 files changed, 6 insertions, 6 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 99a22f44c32e..b6d5adcee8fc 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. */