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Date: Thu, 19 Jan 2012 10:50:40 +0300
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Suresh Siddha <suresh.b.siddha@...el.com>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ming Lei <tom.leiming@...il.com>,
Djalal Harouni <tixxdz@...ndz.org>,
Borislav Petkov <borislav.petkov@....com>,
Tony Luck <tony.luck@...el.com>,
Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
linux-kernel@...r.kernel.org, Greg Kroah-Hartman <gregkh@...e.de>,
Kay Sievers <kay.sievers@...y.org>,
gouders@...bocholt.fh-gelsenkirchen.de,
Marcos Souza <marcos.mage@...il.com>,
Linux PM mailing list <linux-pm@...r.kernel.org>,
"Rafael J. Wysocki" <rjw@...k.pl>,
"tglx@...utronix.de" <tglx@...utronix.de>,
prasad@...ux.vnet.ibm.com, justinmattock@...il.com,
Jeff Chua <jeff.chua.linux@...il.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Mel Gorman <mgorman@...e.de>,
Gilad Ben-Yossef <gilad@...yossef.com>
Subject: Re: x86/mce: machine check warning during poweroff
On (01/18/12 14:08), Suresh Siddha wrote:
> On Wed, 2012-01-18 at 16:32 +0300, Sergey Senozhatsky wrote:
> > Just a small note, since you're talking about removing CPU from nohz.idle_cpus_mask,
> > that I'm able to reproduce this problem not only when offlining CPU, but during
> > onlininig as well (kernel 3.3):
>
> yes, if the nohz state is not cleared properly during offline, then the
> issue can happen any time including cpu online etc.
>
Oh, sure. Good point.
Works for me, here is my:
Tested-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Sergey
> Srivatsa, I thought CPU_PRI_SCHED_INACTIVE as INT_MAX for some reason
> and was expecting sched_ilb_notifier() will be called after setting that
> cpu as inactive. I am now using CPU_DYING which will be called from the
> cpu going down.
>
> Here is the v2 version of the fix. Can you folks please give it another
> try?
>
> Thanks.
> ---
>
> From: Suresh Siddha <suresh.b.siddha@...el.com>
> Subject: sched, nohz: fix nohz cpu idle load balancing state with cpu hotplug
>
> With the recent nohz scheduler changes, rq's nohz flag 'NOHZ_TICK_STOPPED'
> and its associated state doesn't get cleared immediately after the
> cpu exits idle. This gets cleared as part of the next tick seen on that cpu.
>
> With the cpu offline, we need to clear this state manually. Fix it by
> registering a cpu notifier which clears the nohz idle load balance
> state for this rq explicitly.
>
> Reported-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
> kernel/sched/fair.c | 34 +++++++++++++++++++++++++++++-----
> 1 files changed, 29 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 2237ffe..f605e1d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4843,6 +4843,15 @@ static void nohz_balancer_kick(int cpu)
> return;
> }
>
> +static inline void clear_nohz_tick_stopped(int cpu)
> +{
> + if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
> + cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
> + atomic_dec(&nohz.nr_cpus);
> + clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
> + }
> +}
> +
> static inline void set_cpu_sd_state_busy(void)
> {
> struct sched_domain *sd;
> @@ -4881,6 +4890,12 @@ void select_nohz_load_balancer(int stop_tick)
> {
> int cpu = smp_processor_id();
>
> + /*
> + * If this cpu is going down, then nothing needs to be done.
> + */
> + if (!cpu_active(cpu))
> + return;
> +
> if (stop_tick) {
> if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
> return;
> @@ -4891,6 +4906,18 @@ void select_nohz_load_balancer(int stop_tick)
> }
> return;
> }
> +
> +static int __cpuinit sched_ilb_notifier(struct notifier_block *nfb,
> + unsigned long action, void *hcpu)
> +{
> + switch (action & ~CPU_TASKS_FROZEN) {
> + case CPU_DYING:
> + clear_nohz_tick_stopped(smp_processor_id());
> + return NOTIFY_OK;
> + default:
> + return NOTIFY_DONE;
> + }
> +}
> #endif
>
> static DEFINE_SPINLOCK(balancing);
> @@ -5047,11 +5074,7 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
> * busy tick after returning from idle, we will update the busy stats.
> */
> set_cpu_sd_state_busy();
> - if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
> - clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
> - cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
> - atomic_dec(&nohz.nr_cpus);
> - }
> + clear_nohz_tick_stopped(cpu);
>
> /*
> * None are in tickless mode and hence no need for NOHZ idle load
> @@ -5549,6 +5572,7 @@ __init void init_sched_fair_class(void)
>
> #ifdef CONFIG_NO_HZ
> zalloc_cpumask_var(&nohz.idle_cpus_mask, GFP_NOWAIT);
> + cpu_notifier(sched_ilb_notifier, 0);
> #endif
> #endif /* SMP */
>
>
>
--
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