Messages in this thread | | | Date | Mon, 6 Jul 2020 10:06:49 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tick-sched] Clarify "NOHZ: local_softirq_pending" warning |
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On Mon, Jul 06, 2020 at 12:48:16PM -0400, Qian Cai wrote: > On Fri, Jun 26, 2020 at 02:05:06PM -0700, Paul E. McKenney wrote: > > Currently, can_stop_idle_tick() prints "NOHZ: local_softirq_pending HH" > > (where "HH" is the hexadecimal softirq vector number) when one or more > > non-RCU softirq handlers are still enablded when checking to stop the > > scheduler-tick interrupt. This message is not as enlightening as one > > might hope, so this commit changes it to "NOHZ tick-stop error: Non-RCU > > local softirq work is pending, handler #HH. > > > > Reported-by: Andy Lutomirski <luto@kernel.org> > > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > > CPU hotplug will sometimes trigger this warning on linux-next from NUMA > bare-metal which the commit makes it feel more like errors.
One point of the change was to make it clear that this is an error. So success! ;-)
> [ 267.734981] smpboot: CPU 42 is now offline > [ 267.991940] smpboot: Booting Node 2 Processor 42 APIC 0x29 > [ 267.998370] numa_add_cpu cpu 42 node 2: mask now 8-11,40-43 > [ 268.092380] ACPI: \_SB_.SCK0.C015: Found 2 idle states > [ 268.181917] NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #282 > [ 268.190585] numa_remove_cpu cpu 1 node 0: mask now 0,2-3,32-35 > [ 268.194075] smpboot: CPU 1 is now offline > [ 268.415320] x86: Booting SMP configuration: > [ 268.420245] smpboot: Booting Node 0 Processor 1 APIC 0x2 > > # git clone https://github.com/cailca/linux-mm > # cd linux-mm; make > # ./random 4 (it just soft offline and online each CPU) > > The x86.config is also included there. This is only reproducible on x86 > so far.
I must defer to Frederic and Andy on this one. But now that you mention it, I do see this on some of my runs, which are x86, but not bare metal. I clearly need to upgrade my console-log parsing.
Thanx, Paul
> > --- > > > > tick-sched.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > index f0199a4..349a25a 100644 > > --- a/kernel/time/tick-sched.c > > +++ b/kernel/time/tick-sched.c > > @@ -927,7 +927,7 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) > > > > if (ratelimit < 10 && > > (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { > > - pr_warn("NOHZ: local_softirq_pending %02x\n", > > + pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x\n", > > (unsigned int) local_softirq_pending()); > > ratelimit++; > > }
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