-From 98e09386c0ef4dfd48af7ba60ff908f0d525cdee Mon Sep 17 00:00:00 2001
-From: Eric Dumazet <edumazet@google.com>
-Date: Wed, 13 Nov 2013 14:32:54 +0000
-Subject: tcp: tsq: restore minimal amount of queueing
-
-After commit c9eeec26e32e ("tcp: TSQ can use a dynamic limit"), several
-users reported throughput regressions, notably on mvneta and wifi
-adapters.
-
-802.11 AMPDU requires a fair amount of queueing to be effective.
-
-This patch partially reverts the change done in tcp_write_xmit()
-so that the minimal amount is sysctl_tcp_limit_output_bytes.
-
-It also remove the use of this sysctl while building skb stored
-in write queue, as TSO autosizing does the right thing anyway.
-
-Users with well behaving NICS and correct qdisc (like sch_fq),
-can then lower the default sysctl_tcp_limit_output_bytes value from
-128KB to 8KB.
-
-This new usage of sysctl_tcp_limit_output_bytes permits each driver
-authors to check how their driver performs when/if the value is set
-to a minimum of 4KB.
-
-Normally, line rate for a single TCP flow should be possible,
-but some drivers rely on timers to perform TX completion and
-too long TX completion delays prevent reaching full throughput.
-
-Fixes: c9eeec26e32e ("tcp: TSQ can use a dynamic limit")
-Signed-off-by: Eric Dumazet <edumazet@google.com>
-Reported-by: Sujith Manoharan <sujith@msujith.org>
-Reported-by: Arnaud Ebalard <arno@natisbad.org>
-Tested-by: Sujith Manoharan <sujith@msujith.org>
-Cc: Felix Fietkau <nbd@openwrt.org>
-Signed-off-by: David S. Miller <davem@davemloft.net>
----
---- a/Documentation/networking/ip-sysctl.txt
-+++ b/Documentation/networking/ip-sysctl.txt
-@@ -571,9 +571,6 @@ tcp_limit_output_bytes - INTEGER
- typical pfifo_fast qdiscs.
- tcp_limit_output_bytes limits the number of bytes on qdisc
- or device to reduce artificial RTT/cwnd and reduce bufferbloat.
-- Note: For GSO/TSO enabled flows, we try to have at least two
-- packets in flight. Reducing tcp_limit_output_bytes might also
-- reduce the size of individual GSO packet (64KB being the max)
- Default: 131072
-
- tcp_challenge_ack_limit - INTEGER
---- a/net/ipv4/tcp.c
-+++ b/net/ipv4/tcp.c
-@@ -807,12 +807,6 @@ static unsigned int tcp_xmit_size_goal(s
- xmit_size_goal = min_t(u32, gso_size,
- sk->sk_gso_max_size - 1 - hlen);
-
-- /* TSQ : try to have at least two segments in flight
-- * (one in NIC TX ring, another in Qdisc)
-- */
-- xmit_size_goal = min_t(u32, xmit_size_goal,
-- sysctl_tcp_limit_output_bytes >> 1);
--
- xmit_size_goal = tcp_bound_to_half_wnd(tp, xmit_size_goal);
-
- /* We try hard to avoid divides here */
---- a/net/ipv4/tcp_output.c
-+++ b/net/ipv4/tcp_output.c
-@@ -1866,8 +1866,12 @@ static bool tcp_write_xmit(struct sock *
- * - better RTT estimation and ACK scheduling
- * - faster recovery
- * - high rates
-+ * Alas, some drivers / subsystems require a fair amount
-+ * of queued bytes to ensure line rate.
-+ * One example is wifi aggregation (802.11 AMPDU)
- */
-- limit = max(skb->truesize, sk->sk_pacing_rate >> 10);
-+ limit = max_t(unsigned int, sysctl_tcp_limit_output_bytes,
-+ sk->sk_pacing_rate >> 10);
-
- if (atomic_read(&sk->sk_wmem_alloc) > limit) {
- set_bit(TSQ_THROTTLED, &tp->tsq_flags);
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