From: Russell King - ARM Linux <linux@arm•linux.org.uk>
To: Marc Zyngier <marc.zyngier@arm•com>
Cc: "Rafael J. Wysocki" <rafael@kernel•org>,
"linux-pm@vger•kernel.org" <linux-pm@vger•kernel.org>,
Peter Zijlstra <peterz@infradead•org>,
Viresh Kumar <viresh.kumar@linaro•org>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel•com>,
Linux Kernel Mailing List <linux-kernel@vger•kernel.org>,
linux-next@vger•kernel.org, Guenter Roeck <linux@roeck-us•net>,
"linux-arm-kernel@lists•infradead.org"
<linux-arm-kernel@lists•infradead.org>
Subject: Re: Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...'
Date: Mon, 15 Feb 2016 19:23:17 +0000 [thread overview]
Message-ID: <20160215192316.GO10826@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <56C22105.6050900@arm.com>
On Mon, Feb 15, 2016 at 07:03:33PM +0000, Marc Zyngier wrote:
> On 15/02/16 18:54, Rafael J. Wysocki wrote:
> > That would explain it, thanks.
> >
> > So it looks like we should always use irq_work_queue() on UP even if
> > CONFIG_SMP is set, shouldn't we?
>
> Something like that, yes. CONFIG_SMP is not an indication of an SMP
> system anymore (we've even dropped the config option on arm64).
>
> Hopefully num_possible_cpus() is reliable enough to let you do the right
> thing...
CONFIG_SMP just says whether to include support for SMP. It doesn't
mandate running on a SMP system. :)
I've been looking around the usages of irq_work_queue_on in kernel/
in -rc4, and some places seem to check for "this CPU":
/*
* It is possible that a restart caused this CPU to be
* chosen again. Don't bother with an IPI, just see if we
* have more to push.
*/
if (unlikely(cpu == rq->cpu))
goto again;
/* Try the next RT overloaded CPU */
irq_work_queue_on(&rt_rq->push_work, cpu);
I'm not sure about tell_cpu_to_push().
It's also called via tick_nohz_full_kick_cpu(), and the core scheduler
avoids calling this for the current CPU:
if (tick_nohz_full_cpu(cpu)) {
if (cpu != smp_processor_id() ||
tick_nohz_tick_stopped())
tick_nohz_full_kick_cpu(cpu);
I'm not sure about add_nr_running() in kernel/sched/sched.h - I think
that _could_ be a problem even without Rafael's cpufreq change.
So... the question is what do we do with irq_work_queue_on() in general
when called on non-SMP systems.
--
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.
next prev parent reply other threads:[~2016-02-15 19:23 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-15 17:05 Crashes in arm qemu emulations due to 'cpufreq: governor: Replace timers with utilization ...' Guenter Roeck
2016-02-15 18:41 ` Rafael J. Wysocki
2016-02-15 18:49 ` Rafael J. Wysocki
2016-02-15 18:49 ` Marc Zyngier
2016-02-15 18:54 ` Rafael J. Wysocki
2016-02-15 19:03 ` Marc Zyngier
2016-02-15 19:12 ` Rafael J. Wysocki
2016-02-15 19:28 ` Rafael J. Wysocki
2016-02-15 19:42 ` Tony Lindgren
2016-02-15 19:46 ` Guenter Roeck
2016-02-15 19:57 ` Tony Lindgren
2016-02-15 19:23 ` Russell King - ARM Linux [this message]
2016-02-15 20:41 ` Rafael J. Wysocki
2016-02-15 19:07 ` Russell King - ARM Linux
2016-02-15 19:01 ` Tony Lindgren
2016-02-15 19:40 ` Guenter Roeck
2016-02-15 19:58 ` Tony Lindgren
2016-02-15 20:09 ` Guenter Roeck
2016-02-15 20:38 ` Rafael J. Wysocki
2016-02-15 20:37 ` Rafael J. Wysocki
2016-02-15 21:36 ` Tony Lindgren
2016-02-16 1:38 ` Guenter Roeck
2016-02-15 19:02 ` Russell King - ARM Linux
2016-02-16 1:13 ` Viresh Kumar
2016-02-16 1:27 ` Rafael J. Wysocki
2016-02-16 1:36 ` Viresh Kumar
2016-02-15 22:29 ` Peter Maydell
2016-02-15 23:19 ` Guenter Roeck
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