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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 21:59:20 +0200
commit1f649f03683a908fb51ab40ab176c3902f14d335 (patch)
treee1d7957fbe2fc88c13bda617a0e5283ddf7770db
parent7507c7e11351c4dde218f1bc8bc9fce98329a5fa (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>
-rw-r--r--kernel/softirq.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 490fcbb1dc5b..93be750348c8 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -657,9 +657,13 @@ static void run_ksoftirqd(unsigned int cpu)
* in the task stack here.
*/
__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();