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() &&
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.