46 lines
1.8 KiB
Diff
46 lines
1.8 KiB
Diff
From bf1b7f42bc9f739693ff39eb8fc4cc2acb239c0b Mon Sep 17 00:00:00 2001
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Message-Id: <bf1b7f42bc9f739693ff39eb8fc4cc2acb239c0b.1596234183.git.zanussi@kernel.org>
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In-Reply-To: <378ee68279f6a7631221f2670a9298620148690d.1596234183.git.zanussi@kernel.org>
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References: <378ee68279f6a7631221f2670a9298620148690d.1596234183.git.zanussi@kernel.org>
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Wed, 30 Mar 2016 13:36:29 +0200
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Subject: [PATCH 200/329] net: dev: always take qdisc's busylock in
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__dev_xmit_skb()
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.135-rt60.tar.xz
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The root-lock is dropped before dev_hard_start_xmit() is invoked and after
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setting the __QDISC___STATE_RUNNING bit. If this task is now pushed away
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by a task with a higher priority then the task with the higher priority
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won't be able to submit packets to the NIC directly instead they will be
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enqueued into the Qdisc. The NIC will remain idle until the task(s) with
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higher priority leave the CPU and the task with lower priority gets back
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and finishes the job.
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If we take always the busylock we ensure that the RT task can boost the
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low-prio task and submit the packet.
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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net/core/dev.c | 4 ++++
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1 file changed, 4 insertions(+)
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diff --git a/net/core/dev.c b/net/core/dev.c
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index bd2d4195d238..fcaef21a42c3 100644
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--- a/net/core/dev.c
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+++ b/net/core/dev.c
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@@ -3464,7 +3464,11 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
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* This permits qdisc->running owner to get the lock more
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* often and dequeue packets faster.
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*/
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+#ifdef CONFIG_PREEMPT_RT_FULL
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+ contended = true;
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+#else
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contended = qdisc_is_running(q);
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+#endif
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if (unlikely(contended))
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spin_lock(&q->busylock);
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--
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2.17.1
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