On 08/24/2018 02:01 AM, Thomas Gleixner wrote:
> On Fri, 24 Aug 2018, Greg KH wrote:
>> On Thu, Aug 23, 2018 at 05:57:06PM -0500, Grygorii Strashko wrote:
>>> This patch was back ported to the Stable linux-4.14.y and It causes regression -
>>> flood of "NOHZ: local_softirq_pending" messages on all TI boards during boot (NFS boot):
>>>
>>> [ 4.179796] NOHZ: local_softirq_pending 2c2 in sirq 256
>>> [ 4.185051] NOHZ: local_softirq_pending 2c2 in sirq 256
>
> This printout is weird. Did you add something here?
yes.
ff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index da74d2f..a5fad1c 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -910,8 +910,9 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
if (ratelimit < 100 &&
(local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
- pr_warn("NOHZ: local_softirq_pending %02x in sirq %d\n",
+ pr_warn("NOHZ: local_softirq_pending %02x in sirq %lu\n",
(unsigned int) local_softirq_pending(), in_softirq());
+ WARN_ON_ONCE(true);
ratelimit++;
}
>
>>> the same is not reproducible with LKML - seems due to changes in tick-sched.c
>>> __tick_nohz_idle_enter()/tick_nohz_irq_exit().
>>
>> What changes do you think fixed this?
>>
>>> I've generated backtrace from can_stop_idle_tick() (see below) and seems this
>>> patch makes tick_nohz_irq_exit() call unconditional in case of nested interrupt:
>>>
>>> gic_handle_irq
>>> |- irq_exit
>>> |- preempt_count_sub(HARDIRQ_OFFSET); <-- [1]
>>> |-__do_softirq
>>> <irqs enabled>
>>> |- gic_handle_irq()
>>> |- irq_exit()
>>> |- tick_irq_exit()
>>> if (!in_irq()) <-- My understanding is that this condition will be always true due to [1]
>
> Correct, but that's not the problem. The issue is that this happens in a
> softirq disabled region. Does the below fix it?
>
> Thanks,
>
> tglx
>
> 8<--------------------
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 5b33e2f5c0ed..6aab9d54a331 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -888,7 +888,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
> if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
> static int ratelimit;
>
> - if (ratelimit < 10 &&
> + if (ratelimit < 10 && !in_softirq() &&
> (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
> pr_warn("NOHZ: local_softirq_pending %02x\n",
> (unsigned int) local_softirq_pending());
>
>
Yes. i do not see local_softirq_pending messages any more
But one question, just to clarify, after patch "nohz: Fix missing tick reprog while interrupting inline timer softirq"
the tick_nohz_irq_exit() will be called few times in case of nested interrupts (min 2):
gic_handle_irq
|- irq_exit
|- preempt_count_sub(HARDIRQ_OFFSET);
|-__do_softirq
<irqs enabled>
|- gic_handle_irq()
|- irq_exit()
|- tick_irq_exit()
if (!in_irq())
tick_nohz_irq_exit(); <-- [1]
|- tick_irq_exit()
if (!in_irq())
tick_nohz_irq_exit(); <-- [2]
Is it correct? in 4.14 tick_nohz_irq_exit() is much more complex then in LKML now,
and this is hot path.
--
regards,
-grygorii
