| Message ID | 1425093785-27380-3-git-send-email-fan.du@intel.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
> 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; > } A couple things: the local variable probe_size here is TCP segment size, while search_low and search_high are IP datagram sizes. Use tcp_mtu_to_mss to subtract headers. Also, I think if you set sysctl_tcp_probe_threshold <= 0, this will keep probing indefinitely at search_low (not useful). You probably want to test interval < max(1, sysctl_tcp_probe_threshold). -John -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
于 2015年03月01日 07:20, John Heffner 写道: >> 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; >> } > > A couple things: the local variable probe_size here is TCP segment > size, while search_low and search_high are IP datagram sizes. Use > tcp_mtu_to_mss to subtract headers. Also, I think if you set > sysctl_tcp_probe_threshold <= 0, this will keep probing indefinitely > at search_low (not useful). You probably want to test interval < > max(1, sysctl_tcp_probe_threshold). Thanks for the comments, will update in next version. btw, I'm little confused about two points here: 1. Checking if there is enough user data available in write queue with size_needed, Is there any special consideration here involving (tp->reordering + 1) * tp->mss_cache ? Since the assembly always copies "probe_size" bytes data from the write queue. size_needed = probe_size + (tp->reordering + 1) * tp->mss_cache; 2. Traverse write queue to build probing packet with "probe_size" bytes segment, when will the final nskb len exceeding probe_size? which trigger the break in line:1971 1971 if (len >= probe_size) 1972 break; 1973 } 1974 tcp_init_tso_segs(sk, nskb, nskb->len); > -John > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; }
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 <fan.du@intel.com> --- 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(-)