From: robin.murphy@arm.com (Robin Murphy)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v3 1/2] ARM: tango: add HOTPLUG_CPU support
Date: Tue, 28 Jun 2016 16:16:50 +0100 [thread overview]
Message-ID: <577294E2.5030405@arm.com> (raw)
In-Reply-To: <577291F1.8060105@sigmadesigns.com>
On 28/06/16 16:04, Marc Gonzalez wrote:
> On 28/06/2016 14:30, Robin Murphy wrote:
>
>> On 28/06/16 12:59, Marc Gonzalez wrote:
>>
>>> +#ifdef CONFIG_HOTPLUG_CPU
>>> +/*
>>> + * cpu_kill() and cpu_die() run concurrently on different cores.
>>> + * Firmware will only "kill" a core once it has properly "died".
>>> + * Keep trying to kill a core until the operation succeeds, but
>>> + * sleep between tries to give the core time to die.
>>> + */
>>> +static int tango_cpu_kill(unsigned int cpu)
>>> +{
>>> + do {
>>> + msleep(10);
>>> + } while (tango_aux_core_kill(cpu) != 0);
>>
>> Does the firmware guarantee that this will succeed (or at least report
>> success) in finite time, regardless of how messed up the system might
>> be? I'd imagine this should probably have either a timeout or a comment
>> clarifying why it doesn't need a timeout.
>
> Good point.
>
> The FW allows only one thread at a time. If a thread is wedged inside
> the FW, no other thread can use the FW. In that situation, cpu0 would
> remain stuck inside tango_cpu_kill().
>
> Note, that if tango_cpu_kill() starts failing, then secondary cores
> will remain "zombies". So the system is mostly hosed anyway...
> Only cpu0 will be available.
Indeed; my thought was that if CPU1 somehow ends up wedged such that
tango_aux_core_die() never completes, then CPU0 eventually timing out
and being able to limp through a clean(ish) reboot is probably
preferable to spinning in cpu_kill() forever.
Robin.
>
> Regards.
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
next prev parent reply other threads:[~2016-06-28 15:16 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-28 11:55 [PATCH v3 0/2] [for arm-soc] mach-tango updates for v4.8 Marc Gonzalez
2016-06-28 11:59 ` [PATCH v3 1/2] ARM: tango: add HOTPLUG_CPU support Marc Gonzalez
2016-06-28 12:30 ` Robin Murphy
2016-06-28 15:04 ` Marc Gonzalez
2016-06-28 15:16 ` Robin Murphy [this message]
2016-06-29 12:28 ` Marc Gonzalez
2016-06-29 12:21 ` [PATCH v4 " Marc Gonzalez
2016-06-28 12:01 ` [PATCH v3 2/2] Update ARM/TANGO section Marc Gonzalez
2016-07-05 12:32 ` [PATCH v3 0/2] [for arm-soc] mach-tango updates for v4.8 Mason
2016-07-06 3:57 ` Olof Johansson
2016-07-06 20:04 ` Arnd Bergmann
2016-07-07 4:45 ` Olof Johansson
2016-07-07 8:50 ` Mason
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