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authorCalvin Owens <calvinowens@fb.com>2015-01-13 13:16:18 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-05-06 21:56:27 +0200
commit61ea92b94820a4728f6ad1316a22d9dc0b9b4289 (patch)
tree43dd7a92ad9e5d262f197ae9e834fbbbfe7512d8 /kernel
parent3b388f33a1fc643f5e9dc496c741eafdf6ebef49 (diff)
ksoftirqd: Enable IRQs and call cond_resched() before poking RCU
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@fb.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Mike Galbraith <mgalbraith@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/softirq.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 787b3a032429..21956f00cb51 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -774,9 +774,13 @@ static void run_ksoftirqd(unsigned int cpu)
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();