The existing mechanism for detecting thin streams (tcp_stream_is_thin)
is based on a static limit of less than 4 packets in flight. This treats
streams differently depending on the connections RTT, such that a stream
on a high RTT link may never be considered thin, whereas the same
application would produce a stream that would always be thin in a low RTT
scenario (e.g. data center).
By calculating a dynamic packets in flight limit (DPIFL), the thin stream
detection will be independent of the RTT and treat streams equally based
on the transmission pattern, i.e. the inter-transmission time (ITT).
Cc: Andreas Petlund <apetl...@simula.no>
Cc: Carsten Griwodz <gr...@simula.no>
Cc: Pål Halvorsen <pa...@simula.no>
Cc: Jonas Markussen <jona...@ifi.uio.no>
Cc: Kristian Evensen <kristian.even...@gmail.com>
Cc: Kenneth Klette Jonassen <kenne...@ifi.uio.no>
Signed-off-by: Bendik Rønning Opstad <bro.devel+ker...@gmail.com>
---
Documentation/networking/ip-sysctl.txt | 8 ++++++++
include/linux/tcp.h | 6 ++++++
include/net/tcp.h | 20 ++++++++++++++++++++
net/ipv4/sysctl_net_ipv4.c | 9 +++++++++
net/ipv4/tcp.c | 3 +++
5 files changed, 46 insertions(+)
diff --git a/Documentation/networking/ip-sysctl.txt
b/Documentation/networking/ip-sysctl.txt
index 85752c8..b841a76 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -700,6 +700,14 @@ tcp_thin_dupack - BOOLEAN
Documentation/networking/tcp-thin.txt
Default: 0
+tcp_thin_dpifl_itt_lower_bound - INTEGER
+ Controls the lower bound for ITT (inter-transmission time) threshold
+ for when a stream is considered thin. The value is specified in
+ microseconds, and may not be lower than 10000 (10 ms). This theshold
+ is used to calculate a dynamic packets in flight limit (DPIFL) which
+ is used to classify whether a stream is thin.
+ Default: 10000
+
tcp_limit_output_bytes - INTEGER
Controls TCP Small Queue limit per tcp socket.
TCP bulk sender tends to increase packets in flight until it
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index c906f45..fc885db 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -269,6 +269,12 @@ struct tcp_sock {
struct sk_buff* lost_skb_hint;
struct sk_buff *retransmit_skb_hint;
+ /* The limit used to identify when a stream is thin based in a minimum
+ * allowed inter-transmission time (ITT) in microseconds. This is used
+ * to dynamically calculate a max packets in flight limit (DPIFL).
+ */
+ int thin_dpifl_itt_lower_bound;
+
/* OOO segments go in this list. Note that socket lock must be held,
* as we do not use sk_buff_head lock.
*/
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 4fc457b..6534836 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -215,6 +215,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo);
/* TCP thin-stream limits */
#define TCP_THIN_LINEAR_RETRIES 6 /* After 6 linear retries, do exp.
backoff */
+#define TCP_THIN_DPIFL_ITT_LOWER_BOUND_MIN 10000 /* Minimum lower bound is 10
ms (10000 usec) */
/* TCP initial congestion window as per draft-hkchu-tcpm-initcwnd-01 */
#define TCP_INIT_CWND 10
@@ -274,6 +275,7 @@ extern int sysctl_tcp_workaround_signed_windows;
extern int sysctl_tcp_slow_start_after_idle;
extern int sysctl_tcp_thin_linear_timeouts;
extern int sysctl_tcp_thin_dupack;
+extern int sysctl_tcp_thin_dpifl_itt_lower_bound;
extern int sysctl_tcp_early_retrans;
extern int sysctl_tcp_limit_output_bytes;
extern int sysctl_tcp_challenge_ack_limit;
@@ -1631,6 +1633,24 @@ static inline bool tcp_stream_is_thin(struct tcp_sock
*tp)
return tp->packets_out < 4 && !tcp_in_initial_slowstart(tp);
}
+/**
+ * tcp_stream_is_thin_dpifl() - Tests if the stream is thin based on dynamic
PIF
+ * limit
+ * @tp: the tcp_sock struct
+ *
+ * Return: true if current packets in flight (PIF) count is lower than
+ * the dynamic PIF limit, else false
+ */
+static inline bool tcp_stream_is_thin_dpifl(const struct tcp_sock *tp)
+{
+ u64 dpif_lim = tp->srtt_us >> 3;
+ /* Div by is_thin_min_itt_lim, the minimum allowed ITT
+ * (Inter-transmission time) in usecs.
+ */
+ do_div(dpif_lim, tp->thin_dpifl_itt_lower_bound);
+ return tcp_packets_in_flight(tp) < dpif_lim;
+}
+
/* /proc */
enum tcp_seq_states {
TCP_SEQ_STATE_LISTENING,
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 25300c5..917fdde 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -42,6 +42,7 @@ static int tcp_syn_retries_min = 1;
static int tcp_syn_retries_max = MAX_TCP_SYNCNT;
static int ip_ping_group_range_min[] = { 0, 0 };
static int ip_ping_group_range_max[] = { GID_T_MAX, GID_T_MAX };
+static int tcp_thin_dpifl_itt_lower_bound_min =
TCP_THIN_DPIFL_ITT_LOWER_BOUND_MIN;
/* Update system visible IP port range */
static void set_local_port_range(struct net *net, int range[2])
@@ -709,6 +710,14 @@ static struct ctl_table ipv4_table[] = {
.proc_handler = proc_dointvec
},
{
+ .procname = "tcp_thin_dpifl_itt_lower_bound",
+ .data = &sysctl_tcp_thin_dpifl_itt_lower_bound,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec_minmax,
+ .extra1 = &tcp_thin_dpifl_itt_lower_bound_min,
+ },
+ {
.procname = "tcp_early_retrans",
.data = &sysctl_tcp_early_retrans,
.maxlen = sizeof(int),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 0cfa7c0..f712d7c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -287,6 +287,8 @@ int sysctl_tcp_min_tso_segs __read_mostly = 2;
int sysctl_tcp_autocorking __read_mostly = 1;
+int sysctl_tcp_thin_dpifl_itt_lower_bound __read_mostly =
TCP_THIN_DPIFL_ITT_LOWER_BOUND_MIN;
+
struct percpu_counter tcp_orphan_count;
EXPORT_SYMBOL_GPL(tcp_orphan_count);
@@ -406,6 +408,7 @@ void tcp_init_sock(struct sock *sk)
u64_stats_init(&tp->syncp);
tp->reordering = sysctl_tcp_reordering;
+ tp->thin_dpifl_itt_lower_bound = sysctl_tcp_thin_dpifl_itt_lower_bound;
tcp_enable_early_retrans(tp);
tcp_assign_congestion_control(sk);
--
1.9.1
--
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