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