ksoftirqd: Enable IRQs and call cond_resched() before poking RCU
commit28423ad283
upstream. While debugging an issue with excessive softirq usage, I encountered the following note in commit3e339b5dae
("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>
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@ -657,9 +657,13 @@ static void run_ksoftirqd(unsigned int cpu)
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* in the task stack here.
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*/
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__do_softirq();
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rcu_note_context_switch(cpu);
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local_irq_enable();
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cond_resched();
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preempt_disable();
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rcu_note_context_switch(cpu);
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preempt_enable();
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return;
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}
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local_irq_enable();
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