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authorDavid S. Miller <davem@davemloft.net>2012-07-10 03:07:30 +0400
committerDavid S. Miller <davem@davemloft.net>2012-07-11 07:31:36 +0400
commit4aabd8ef8c43677cfee3e1e36c5a79edddb41942 (patch)
treea826352ad00ffcc1632edecfe4ebd77db1301e4b /net/ipv4/tcp_metrics.c
parentad7eee98bef92481581060801bdfd1b25a6106c0 (diff)
downloadlinux-4aabd8ef8c43677cfee3e1e36c5a79edddb41942.tar.xz
tcp: Move dynamnic metrics handling into seperate file.
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_metrics.c')
-rw-r--r--net/ipv4/tcp_metrics.c192
1 files changed, 192 insertions, 0 deletions
diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
new file mode 100644
index 000000000000..2793ecf928d3
--- /dev/null
+++ b/net/ipv4/tcp_metrics.c
@@ -0,0 +1,192 @@
+#include <linux/cache.h>
+#include <linux/tcp.h>
+
+#include <net/inet_connection_sock.h>
+#include <net/sock.h>
+#include <net/dst.h>
+#include <net/tcp.h>
+
+int sysctl_tcp_nometrics_save __read_mostly;
+
+/* Save metrics learned by this TCP session. This function is called
+ * only, when TCP finishes successfully i.e. when it enters TIME-WAIT
+ * or goes from LAST-ACK to CLOSE.
+ */
+void tcp_update_metrics(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct dst_entry *dst = __sk_dst_get(sk);
+
+ if (sysctl_tcp_nometrics_save)
+ return;
+
+ if (dst && (dst->flags & DST_HOST)) {
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ int m;
+ unsigned long rtt;
+
+ dst_confirm(dst);
+
+ if (icsk->icsk_backoff || !tp->srtt) {
+ /* This session failed to estimate rtt. Why?
+ * Probably, no packets returned in time.
+ * Reset our results.
+ */
+ if (!(dst_metric_locked(dst, RTAX_RTT)))
+ dst_metric_set(dst, RTAX_RTT, 0);
+ return;
+ }
+
+ rtt = dst_metric_rtt(dst, RTAX_RTT);
+ m = rtt - tp->srtt;
+
+ /* If newly calculated rtt larger than stored one,
+ * store new one. Otherwise, use EWMA. Remember,
+ * rtt overestimation is always better than underestimation.
+ */
+ if (!(dst_metric_locked(dst, RTAX_RTT))) {
+ if (m <= 0)
+ set_dst_metric_rtt(dst, RTAX_RTT, tp->srtt);
+ else
+ set_dst_metric_rtt(dst, RTAX_RTT, rtt - (m >> 3));
+ }
+
+ if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
+ unsigned long var;
+ if (m < 0)
+ m = -m;
+
+ /* Scale deviation to rttvar fixed point */
+ m >>= 1;
+ if (m < tp->mdev)
+ m = tp->mdev;
+
+ var = dst_metric_rtt(dst, RTAX_RTTVAR);
+ if (m >= var)
+ var = m;
+ else
+ var -= (var - m) >> 2;
+
+ set_dst_metric_rtt(dst, RTAX_RTTVAR, var);
+ }
+
+ if (tcp_in_initial_slowstart(tp)) {
+ /* Slow start still did not finish. */
+ if (dst_metric(dst, RTAX_SSTHRESH) &&
+ !dst_metric_locked(dst, RTAX_SSTHRESH) &&
+ (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
+ dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_cwnd >> 1);
+ if (!dst_metric_locked(dst, RTAX_CWND) &&
+ tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
+ dst_metric_set(dst, RTAX_CWND, tp->snd_cwnd);
+ } else if (tp->snd_cwnd > tp->snd_ssthresh &&
+ icsk->icsk_ca_state == TCP_CA_Open) {
+ /* Cong. avoidance phase, cwnd is reliable. */
+ if (!dst_metric_locked(dst, RTAX_SSTHRESH))
+ dst_metric_set(dst, RTAX_SSTHRESH,
+ max(tp->snd_cwnd >> 1, tp->snd_ssthresh));
+ if (!dst_metric_locked(dst, RTAX_CWND))
+ dst_metric_set(dst, RTAX_CWND,
+ (dst_metric(dst, RTAX_CWND) +
+ tp->snd_cwnd) >> 1);
+ } else {
+ /* Else slow start did not finish, cwnd is non-sense,
+ ssthresh may be also invalid.
+ */
+ if (!dst_metric_locked(dst, RTAX_CWND))
+ dst_metric_set(dst, RTAX_CWND,
+ (dst_metric(dst, RTAX_CWND) +
+ tp->snd_ssthresh) >> 1);
+ if (dst_metric(dst, RTAX_SSTHRESH) &&
+ !dst_metric_locked(dst, RTAX_SSTHRESH) &&
+ tp->snd_ssthresh > dst_metric(dst, RTAX_SSTHRESH))
+ dst_metric_set(dst, RTAX_SSTHRESH, tp->snd_ssthresh);
+ }
+
+ if (!dst_metric_locked(dst, RTAX_REORDERING)) {
+ if (dst_metric(dst, RTAX_REORDERING) < tp->reordering &&
+ tp->reordering != sysctl_tcp_reordering)
+ dst_metric_set(dst, RTAX_REORDERING, tp->reordering);
+ }
+ }
+}
+
+/* Initialize metrics on socket. */
+
+void tcp_init_metrics(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct dst_entry *dst = __sk_dst_get(sk);
+
+ if (dst == NULL)
+ goto reset;
+
+ dst_confirm(dst);
+
+ if (dst_metric_locked(dst, RTAX_CWND))
+ tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
+ if (dst_metric(dst, RTAX_SSTHRESH)) {
+ tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
+ if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
+ tp->snd_ssthresh = tp->snd_cwnd_clamp;
+ } else {
+ /* ssthresh may have been reduced unnecessarily during.
+ * 3WHS. Restore it back to its initial default.
+ */
+ tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
+ }
+ if (dst_metric(dst, RTAX_REORDERING) &&
+ tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
+ tcp_disable_fack(tp);
+ tcp_disable_early_retrans(tp);
+ tp->reordering = dst_metric(dst, RTAX_REORDERING);
+ }
+
+ if (dst_metric(dst, RTAX_RTT) == 0 || tp->srtt == 0)
+ goto reset;
+
+ /* Initial rtt is determined from SYN,SYN-ACK.
+ * The segment is small and rtt may appear much
+ * less than real one. Use per-dst memory
+ * to make it more realistic.
+ *
+ * A bit of theory. RTT is time passed after "normal" sized packet
+ * is sent until it is ACKed. In normal circumstances sending small
+ * packets force peer to delay ACKs and calculation is correct too.
+ * The algorithm is adaptive and, provided we follow specs, it
+ * NEVER underestimate RTT. BUT! If peer tries to make some clever
+ * tricks sort of "quick acks" for time long enough to decrease RTT
+ * to low value, and then abruptly stops to do it and starts to delay
+ * ACKs, wait for troubles.
+ */
+ if (dst_metric_rtt(dst, RTAX_RTT) > tp->srtt) {
+ tp->srtt = dst_metric_rtt(dst, RTAX_RTT);
+ tp->rtt_seq = tp->snd_nxt;
+ }
+ if (dst_metric_rtt(dst, RTAX_RTTVAR) > tp->mdev) {
+ tp->mdev = dst_metric_rtt(dst, RTAX_RTTVAR);
+ tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
+ }
+ tcp_set_rto(sk);
+reset:
+ if (tp->srtt == 0) {
+ /* RFC6298: 5.7 We've failed to get a valid RTT sample from
+ * 3WHS. This is most likely due to retransmission,
+ * including spurious one. Reset the RTO back to 3secs
+ * from the more aggressive 1sec to avoid more spurious
+ * retransmission.
+ */
+ tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK;
+ inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
+ }
+ /* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
+ * retransmitted. In light of RFC6298 more aggressive 1sec
+ * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
+ * retransmission has occurred.
+ */
+ if (tp->total_retrans > 1)
+ tp->snd_cwnd = 1;
+ else
+ tp->snd_cwnd = tcp_init_cwnd(tp, dst);
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+}