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authorFrancis Yan <francisyyan@gmail.com>2016-11-27 23:07:13 -0800
committerDavid S. Miller <davem@davemloft.net>2016-11-30 10:04:24 -0500
commit05b055e89121394058c75dc354e9a46e1e765579 (patch)
treef4f070fbc44650c700ab3b57fe3ff35080e4df08
parenta090994980a15f8cc14fc188b5929bd61d2ae9c3 (diff)
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>
-rw-r--r--include/linux/tcp.h7
-rw-r--r--include/net/tcp.h14
-rw-r--r--net/ipv4/tcp_output.c30
3 files changed, 49 insertions, 2 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 32a7c7e..d5d3bd8 100644
--- 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 7de8073..e5ff408 100644
--- 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 19105b4..34f7517 100644
--- 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.