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b2ea46fe23
An overall throughput gain of 22 % for heavy TCP use over a single TX queue. Original patchset comment https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v4.13&id=3f4888adae7c1619b990d98a9b967536f71822b8 Signed-off-by: Pavel Kubelun <be.dissent@gmail.com>
49 lines
1.6 KiB
Diff
49 lines
1.6 KiB
Diff
From 408f0a6c21e124cc4f6c7aa370b38aa47e55428d Mon Sep 17 00:00:00 2001
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From: Eric Dumazet <edumazet@google.com>
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Date: Sat, 3 Dec 2016 11:14:51 -0800
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Subject: [PATCH 02/10] tcp: tsq: remove one locked operation in tcp_wfree()
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Instead of atomically clear TSQ_THROTTLED and atomically set TSQ_QUEUED
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bits, use one cmpxchg() to perform a single locked operation.
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Since the following patch will also set TCP_TSQ_DEFERRED here,
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this cmpxchg() will make this addition free.
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Signed-off-by: Eric Dumazet <edumazet@google.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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---
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net/ipv4/tcp_output.c | 13 ++++++++++---
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1 file changed, 10 insertions(+), 3 deletions(-)
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--- a/net/ipv4/tcp_output.c
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+++ b/net/ipv4/tcp_output.c
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@@ -860,6 +860,7 @@ void tcp_wfree(struct sk_buff *skb)
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{
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struct sock *sk = skb->sk;
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struct tcp_sock *tp = tcp_sk(sk);
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+ unsigned long flags, nval, oval;
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int wmem;
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/* Keep one reference on sk_wmem_alloc.
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@@ -877,11 +878,17 @@ void tcp_wfree(struct sk_buff *skb)
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if (wmem >= SKB_TRUESIZE(1) && this_cpu_ksoftirqd() == current)
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goto out;
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- if (test_and_clear_bit(TSQ_THROTTLED, &tp->tsq_flags) &&
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- !test_and_set_bit(TSQ_QUEUED, &tp->tsq_flags)) {
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- unsigned long flags;
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+ for (oval = READ_ONCE(tp->tsq_flags);; oval = nval) {
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struct tsq_tasklet *tsq;
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+ if (!(oval & TSQF_THROTTLED) || (oval & TSQF_QUEUED))
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+ goto out;
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+
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+ nval = (oval & ~TSQF_THROTTLED) | TSQF_QUEUED;
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+ nval = cmpxchg(&tp->tsq_flags, oval, nval);
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+ if (nval != oval)
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+ continue;
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+
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/* queue this socket to tasklet queue */
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local_irq_save(flags);
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tsq = this_cpu_ptr(&tsq_tasklet);
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