This is a note to let you know that I've just added the patch titled
ksoftirqd: Enable IRQs and call cond_resched() before poking RCU
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
ksoftirqd-enable-irqs-and-call-cond_resched-before-poking-rcu.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 28423ad283d5348793b0c45cc9b1af058e776fd6 Mon Sep 17 00:00:00 2001
From: Calvin Owens <calvinowens@xxxxxx>
Date: Tue, 13 Jan 2015 13:16:18 -0800
Subject: ksoftirqd: Enable IRQs and call cond_resched() before poking RCU
From: Calvin Owens <calvinowens@xxxxxx>
commit 28423ad283d5348793b0c45cc9b1af058e776fd6 upstream.
While debugging an issue with excessive softirq usage, I encountered the
following note in commit 3e339b5dae24a706 ("softirq: Use hotplug thread
infrastructure"):
[ paulmck: Call rcu_note_context_switch() with interrupts enabled. ]
...but despite this note, the patch still calls RCU with IRQs disabled.
This seemingly innocuous change caused a significant regression in softirq
CPU usage on the sending side of a large TCP transfer (~1 GB/s): when
introducing 0.01% packet loss, the softirq usage would jump to around 25%,
spiking as high as 50%. Before the change, the usage would never exceed 5%.
Moving the call to rcu_note_context_switch() after the cond_sched() call,
as it was originally before the hotplug patch, completely eliminated this
problem.
Signed-off-by: Calvin Owens <calvinowens@xxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Mike Galbraith <mgalbraith@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/softirq.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -774,9 +774,13 @@ static void run_ksoftirqd(unsigned int c
local_irq_disable();
if (local_softirq_pending()) {
__do_softirq();
- rcu_note_context_switch(cpu);
local_irq_enable();
cond_resched();
+
+ preempt_disable();
+ rcu_note_context_switch(cpu);
+ preempt_enable();
+
return;
}
local_irq_enable();
Patches currently in stable-queue which might be from calvinowens@xxxxxx are
queue-3.10/ksoftirqd-enable-irqs-and-call-cond_resched-before-poking-rcu.patch
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