| Date | Fri, 1 May 2015 15:00:00 -0500 | Subject | Re: [PATCH 3.19 016/175] ksoftirqd: Enable IRQs and call cond_resched() before poking RCU | From | Josh Hunt <> |
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On Wed, Mar 4, 2015 at 12:13 AM, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > 3.19-stable review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Calvin Owens <calvinowens@fb.com> > > 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > --- > kernel/softirq.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > --- a/kernel/softirq.c > +++ b/kernel/softirq.c > @@ -656,9 +656,13 @@ static void run_ksoftirqd(unsigned int c > * in the task stack here. > */ > __do_softirq(); > - rcu_note_context_switch(); > local_irq_enable(); > cond_resched(); > + > + preempt_disable(); > + rcu_note_context_switch(); > + preempt_enable(); > + > return; > } > local_irq_enable(); > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
Sorry for the delay in noticing this, but should this be applied to 3.14-stable as well?
Thanks Josh
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