tcp: instrument tcp sender limits chronographs

This patch implements the skeleton of the TCP chronograph
instrumentation on sender side limits:

	1) idle (unspec)
	2) busy sending data other than 3-4 below
	3) rwnd-limited
	4) sndbuf-limited

The limits are enumerated 'tcp_chrono'. Since a connection in
theory can idle forever, we do not track the actual length of this
uninteresting idle period. For the rest we track how long the sender
spends in each limit. At any point during the life time of a
connection, the sender must be in one of the four states.

If there are multiple conditions worthy of tracking in a chronograph
then the highest priority enum takes precedence over
the other conditions. So that if something "more interesting"
starts happening, stop the previous chrono and start a new one.

The time unit is jiffy(u32) in order to save space in tcp_sock.
This implies application must sample the stats no longer than every
49 days of 1ms jiffy.

Signed-off-by: Francis Yan <francisyyan@gmail.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 32a7c7e35b715debc9c8df324c9393381f2ae900..d5d3bd814338744f0414063e033c769651418451 100644 (file)
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -211,8 +211,11 @@ struct tcp_sock {
                u8 reord;    /* reordering detected */
        } rack;
        u16     advmss;         /* Advertised MSS                       */
-       u8      rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
-               unused:7;
+       u32     chrono_start;   /* Start time in jiffies of a TCP chrono */
+       u32     chrono_stat[3]; /* Time in jiffies for chrono_stat stats */
+       u8      chrono_type:2,  /* current chronograph type */
+               rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
+               unused:5;
        u8      nonagle     : 4,/* Disable Nagle algorithm?             */
                thin_lto    : 1,/* Use linear timeouts for thin streams */
                thin_dupack : 1,/* Fast retransmit on first dupack      */

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 7de80739adabace8c4d6250cb30021c5dace1b9b..e5ff4083870d29a07c99e817fa8041b841e9e91d 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1516,6 +1516,20 @@ struct tcp_fastopen_context {
        struct rcu_head         rcu;
 };
 
+/* Latencies incurred by various limits for a sender. They are
+ * chronograph-like stats that are mutually exclusive.
+ */
+enum tcp_chrono {
+       TCP_CHRONO_UNSPEC,
+       TCP_CHRONO_BUSY, /* Actively sending data (non-empty write queue) */
+       TCP_CHRONO_RWND_LIMITED, /* Stalled by insufficient receive window */
+       TCP_CHRONO_SNDBUF_LIMITED, /* Stalled by insufficient send buffer */
+       __TCP_CHRONO_MAX,
+};
+
+void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type);
+void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type);
+
 /* write queue abstraction */
 static inline void tcp_write_queue_purge(struct sock *sk)
 {

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 19105b46a30436ebb85fe97ee43089e77aa028bb..34f751776a0138e1af45d387ca53632a20e3f426 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2081,6 +2081,36 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,
        return false;
 }
 
+static void tcp_chrono_set(struct tcp_sock *tp, const enum tcp_chrono new)
+{
+       const u32 now = tcp_time_stamp;
+
+       if (tp->chrono_type > TCP_CHRONO_UNSPEC)
+               tp->chrono_stat[tp->chrono_type - 1] += now - tp->chrono_start;
+       tp->chrono_start = now;
+       tp->chrono_type = new;
+}
+
+void tcp_chrono_start(struct sock *sk, const enum tcp_chrono type)
+{
+       struct tcp_sock *tp = tcp_sk(sk);
+
+       /* If there are multiple conditions worthy of tracking in a
+        * chronograph then the highest priority enum takes precedence over
+        * the other conditions. So that if something "more interesting"
+        * starts happening, stop the previous chrono and start a new one.
+        */
+       if (type > tp->chrono_type)
+               tcp_chrono_set(tp, type);
+}
+
+void tcp_chrono_stop(struct sock *sk, const enum tcp_chrono type)
+{
+       struct tcp_sock *tp = tcp_sk(sk);
+
+       tcp_chrono_set(tp, TCP_CHRONO_UNSPEC);
+}
+
 /* This routine writes packets to the network.  It advances the
  * send_head.  This happens as incoming acks open up the remote
  * window for us.