[Ecn-sane] Fwd: [PATCH net-next 2/5] tcp: add PLB functionality for TCP
Dave Taht
dave.taht at gmail.com
Thu Sep 29 11:03:59 EDT 2022
see: https://henryhxu.github.io/share/jinbin-apnet22.pdf
---------- Forwarded message ---------
From: Mubashir Adnan Qureshi <mubashirmaq at gmail.com>
Date: Thu, Sep 29, 2022 at 7:59 AM
Subject: [PATCH net-next 2/5] tcp: add PLB functionality for TCP
To: David Miller <davem at davemloft.net>
Cc: <netdev at vger.kernel.org>, Mubashir Adnan Qureshi
<mubashirq at google.com>, Yuchung Cheng <ycheng at google.com>, Neal
Cardwell <ncardwell at google.com>, Eric Dumazet <edumazet at google.com>
From: Mubashir Adnan Qureshi <mubashirq at google.com>
Congestion control algorithms track PLB state and cause the connection
to trigger a path change when either of the 2 conditions is satisfied:
- No packets are in flight and (# consecutive congested rounds >=
sysctl_tcp_plb_idle_rehash_rounds)
- (# consecutive congested rounds >= sysctl_tcp_plb_rehash_rounds)
A round (RTT) is marked as congested when congestion signal
(ECN ce_ratio) over an RTT is greater than sysctl_tcp_plb_cong_thresh.
In the event of RTO, PLB (via tcp_write_timeout()) triggers a path
change and disables congestion-triggered path changes for random time
between (sysctl_tcp_plb_suspend_rto_sec, 2*sysctl_tcp_plb_suspend_rto_sec)
to avoid hopping onto the "connectivity blackhole". RTO-triggered
path changes can still happen during this cool-off period.
Signed-off-by: Mubashir Adnan Qureshi <mubashirq at google.com>
Signed-off-by: Yuchung Cheng <ycheng at google.com>
Signed-off-by: Neal Cardwell <ncardwell at google.com>
Reviewed-by: Eric Dumazet <edumazet at google.com>
---
include/net/tcp.h | 28 +++++++++++++
net/ipv4/Makefile | 2 +-
net/ipv4/tcp_plb.c | 102 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 131 insertions(+), 1 deletion(-)
create mode 100644 net/ipv4/tcp_plb.c
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 27e8d378c70a..c50af63addea 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2135,6 +2135,34 @@ extern void tcp_rack_advance(struct tcp_sock
*tp, u8 sacked, u32 end_seq,
extern void tcp_rack_reo_timeout(struct sock *sk);
extern void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs);
+/* tcp_plb.c */
+
+/*
+ * Scaling factor for fractions in PLB. For example, tcp_plb_update_state
+ * expects cong_ratio which represents fraction of traffic that experienced
+ * congestion over a single RTT. In order to avoid floating point operations,
+ * this fraction should be mapped to (1 << TCP_PLB_SCALE) and passed in.
+ */
+#define TCP_PLB_SCALE 8
+
+/* State for PLB (Protective Load Balancing) for a single TCP connection. */
+struct tcp_plb_state {
+ u8 consec_cong_rounds:5, /* consecutive congested rounds */
+ unused:3;
+ u32 pause_until; /* jiffies32 when PLB can resume rerouting */
+};
+
+static inline void tcp_plb_init(const struct sock *sk,
+ struct tcp_plb_state *plb)
+{
+ plb->consec_cong_rounds = 0;
+ plb->pause_until = 0;
+}
+void tcp_plb_update_state(const struct sock *sk, struct tcp_plb_state *plb,
+ const int cong_ratio);
+void tcp_plb_check_rehash(struct sock *sk, struct tcp_plb_state *plb);
+void tcp_plb_update_state_upon_rto(struct sock *sk, struct tcp_plb_state *plb);
+
/* At how many usecs into the future should the RTO fire? */
static inline s64 tcp_rto_delta_us(const struct sock *sk)
{
diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
index bbdd9c44f14e..af7d2cf490fb 100644
--- a/net/ipv4/Makefile
+++ b/net/ipv4/Makefile
@@ -10,7 +10,7 @@ obj-y := route.o inetpeer.o protocol.o \
tcp.o tcp_input.o tcp_output.o tcp_timer.o tcp_ipv4.o \
tcp_minisocks.o tcp_cong.o tcp_metrics.o tcp_fastopen.o \
tcp_rate.o tcp_recovery.o tcp_ulp.o \
- tcp_offload.o datagram.o raw.o udp.o udplite.o \
+ tcp_offload.o tcp_plb.o datagram.o raw.o udp.o udplite.o \
udp_offload.o arp.o icmp.o devinet.o af_inet.o igmp.o \
fib_frontend.o fib_semantics.o fib_trie.o fib_notifier.o \
inet_fragment.o ping.o ip_tunnel_core.o gre_offload.o \
diff --git a/net/ipv4/tcp_plb.c b/net/ipv4/tcp_plb.c
new file mode 100644
index 000000000000..26ffc5a45f53
--- /dev/null
+++ b/net/ipv4/tcp_plb.c
@@ -0,0 +1,102 @@
+/* Protective Load Balancing (PLB)
+ *
+ * PLB was designed to reduce link load imbalance across datacenter
+ * switches. PLB is a host-based optimization; it leverages congestion
+ * signals from the transport layer to randomly change the path of the
+ * connection experiencing sustained congestion. PLB prefers to repath
+ * after idle periods to minimize packet reordering. It repaths by
+ * changing the IPv6 Flow Label on the packets of a connection, which
+ * datacenter switches include as part of ECMP/WCMP hashing.
+ *
+ * PLB is described in detail in:
+ *
+ * Mubashir Adnan Qureshi, Yuchung Cheng, Qianwen Yin, Qiaobin Fu,
+ * Gautam Kumar, Masoud Moshref, Junhua Yan, Van Jacobson,
+ * David Wetherall,Abdul Kabbani:
+ * "PLB: Congestion Signals are Simple and Effective for
+ * Network Load Balancing"
+ * In ACM SIGCOMM 2022, Amsterdam Netherlands.
+ *
+ */
+
+#include <net/tcp.h>
+
+/* Called once per round-trip to update PLB state for a connection. */
+void tcp_plb_update_state(const struct sock *sk, struct tcp_plb_state *plb,
+ const int cong_ratio)
+{
+ struct net *net = sock_net(sk);
+
+ if (!READ_ONCE(net->ipv4.sysctl_tcp_plb_enabled))
+ return;
+
+ if (cong_ratio >= 0) {
+ if (cong_ratio <
READ_ONCE(net->ipv4.sysctl_tcp_plb_cong_thresh))
+ plb->consec_cong_rounds = 0;
+ else if (plb->consec_cong_rounds <
+ READ_ONCE(net->ipv4.sysctl_tcp_plb_rehash_rounds))
+ plb->consec_cong_rounds++;
+ }
+}
+EXPORT_SYMBOL_GPL(tcp_plb_update_state);
+
+/* Check whether recent congestion has been persistent enough to warrant
+ * a load balancing decision that switches the connection to another path.
+ */
+void tcp_plb_check_rehash(struct sock *sk, struct tcp_plb_state *plb)
+{
+ struct net *net = sock_net(sk);
+ bool can_idle_rehash, can_force_rehash;
+ u32 max_suspend;
+
+ if (!READ_ONCE(net->ipv4.sysctl_tcp_plb_enabled))
+ return;
+
+ /* Note that tcp_jiffies32 can wrap; we detect wraps by checking for
+ * cases where the max suspension end is before the actual suspension
+ * end. We clear pause_until to 0 to indicate there is no recent
+ * RTO event that constrains PLB rehashing.
+ */
+ max_suspend = 2 *
READ_ONCE(net->ipv4.sysctl_tcp_plb_suspend_rto_sec) * HZ;
+ if (plb->pause_until &&
+ (!before(tcp_jiffies32, plb->pause_until) ||
+ before(tcp_jiffies32 + max_suspend, plb->pause_until)))
+ plb->pause_until = 0;
+
+ can_idle_rehash =
READ_ONCE(net->ipv4.sysctl_tcp_plb_idle_rehash_rounds) &&
+ !tcp_sk(sk)->packets_out &&
+ plb->consec_cong_rounds >=
+
READ_ONCE(net->ipv4.sysctl_tcp_plb_idle_rehash_rounds);
+ can_force_rehash = plb->consec_cong_rounds >=
+ READ_ONCE(net->ipv4.sysctl_tcp_plb_rehash_rounds);
+
+ if (!plb->pause_until && (can_idle_rehash || can_force_rehash)) {
+ sk_rethink_txhash(sk);
+ plb->consec_cong_rounds = 0;
+ }
+}
+EXPORT_SYMBOL_GPL(tcp_plb_check_rehash);
+
+/* Upon RTO, disallow load balancing for a while, to avoid having load
+ * balancing decisions switch traffic to a black-holed path that was
+ * previously avoided with a sk_rethink_txhash() call at RTO time.
+ */
+void tcp_plb_update_state_upon_rto(struct sock *sk, struct tcp_plb_state *plb)
+{
+ struct net *net = sock_net(sk);
+ u32 pause;
+
+ if (!READ_ONCE(net->ipv4.sysctl_tcp_plb_enabled))
+ return;
+
+ pause = READ_ONCE(net->ipv4.sysctl_tcp_plb_suspend_rto_sec) * HZ;
+ pause += prandom_u32_max(pause);
+ plb->pause_until = tcp_jiffies32 + pause;
+
+ /* Reset PLB state upon RTO, since an RTO causes a
sk_rethink_txhash() call
+ * that may switch this connection to a path with completely different
+ * congestion characteristics.
+ */
+ plb->consec_cong_rounds = 0;
+}
+EXPORT_SYMBOL_GPL(tcp_plb_update_state_upon_rto);
--
2.37.3.998.g577e59143f-goog
--
FQ World Domination pending: https://blog.cerowrt.org/post/state_of_fq_codel/
Dave Täht CEO, TekLibre, LLC
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