[PATCHv3 net-next 2/4] ipv4: Use binary search to choose tcp PMTU probe_size
From: Fan Du <hidden>
Date: 2015-02-28 03:27:53
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
Current probe_size is chosen by doubling mss_cache,
the probing process will end shortly with a sub-optimal
mss size, and the link mtu will not be taken full
advantage of, in return, this will make user to tweak
tcp_base_mss with care.
Use binary search to choose probe_size in a fine
granularity manner, an optimal mss will be found
to boost performance as its maxmium.
In addition, introduce a sysctl_tcp_probe_threshold
to control when probing will stop in respect to
the width of search range.
Test env:
Docker instance with vxlan encapuslation(82599EB)
iperf -c 10.0.0.24 -t 60
before this patch:
1.26 Gbits/sec
After this patch: increase 26%
1.59 Gbits/sec
Signed-off-by: Fan Du <redacted>
---
v3:
- Fix commit message
v2:
- Use sysctl_tcp_probe_threshold to control when probing
will stop wrt interval between search high and search low.
---
include/net/netns/ipv4.h | 1 +
include/net/tcp.h | 3 +++
net/ipv4/sysctl_net_ipv4.c | 7 +++++++
net/ipv4/tcp_ipv4.c | 1 +
net/ipv4/tcp_output.c | 14 +++++++++++---
5 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index dbe2254..25200d4 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h@@ -84,6 +84,7 @@ struct netns_ipv4 { int sysctl_tcp_fwmark_accept; int sysctl_tcp_mtu_probing; int sysctl_tcp_base_mss; + int sysctl_tcp_probe_threshold; struct ping_group_range ping_group_range;
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 7b57e5b..d269c91 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h@@ -67,6 +67,9 @@ void tcp_time_wait(struct sock *sk, int state, int timeo); /* The least MTU to use for probing */ #define TCP_BASE_MSS 1024 +/* Specify interval when tcp mtu probing will stop */ +#define TCP_PROBE_THRESHOLD 8 + /* After receiving this amount of duplicate ACKs fast retransmit starts. */ #define TCP_FASTRETRANS_THRESH 3
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index d151539..d3c09c1 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c@@ -883,6 +883,13 @@ static struct ctl_table ipv4_net_table[] = { .mode = 0644, .proc_handler = proc_dointvec, }, + { + .procname = "tcp_probe_threshold", + .data = &init_net.ipv4.sysctl_tcp_probe_threshold, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec, + }, { } };
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 5a2dfed..35790d9 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c@@ -2460,6 +2460,7 @@ static int __net_init tcp_sk_init(struct net *net) } net->ipv4.sysctl_tcp_ecn = 2; net->ipv4.sysctl_tcp_base_mss = TCP_BASE_MSS; + net->ipv4.sysctl_tcp_probe_threshold = TCP_PROBE_THRESHOLD; return 0; fail:
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index a2a796c..c418829 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c@@ -1837,11 +1837,13 @@ static int tcp_mtu_probe(struct sock *sk) struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); struct sk_buff *skb, *nskb, *next; + struct net *net = sock_net(sk); int len; int probe_size; int size_needed; int copy; int mss_now; + int interval; /* Not currently probing/verifying, * not in recovery,
@@ -1854,11 +1856,17 @@ static int tcp_mtu_probe(struct sock *sk) tp->rx_opt.num_sacks || tp->rx_opt.dsack) return -1; - /* Very simple search strategy: just double the MSS. */ + /* Use binary search for probe_size bewteen tcp_mss_base, + * and current mss_clamp. if (search_high - search_low) + * smaller than a threshold, backoff from probing. + */ mss_now = tcp_current_mss(sk); - probe_size = 2 * tp->mss_cache; + probe_size = (icsk->icsk_mtup.search_high + + icsk->icsk_mtup.search_low) >> 1; size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache; - if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high)) { + interval = icsk->icsk_mtup.search_high - icsk->icsk_mtup.search_low; + if (probe_size > tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_high) || + interval < net->ipv4.sysctl_tcp_probe_threshold) { /* TODO: set timer for probe_converge_event */ return -1; }
--
1.7.1