linux-kernel - Re: [PATCH 2/2] arm64: take onlined cpus into account when setting irq affinity in migrate_one

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Date:	Thu, 28 Aug 2014 16:00:34 +0900
From:	byungchul park <max.byungchul.park@...il.com>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	"byungchul.park@....com" <byungchul.park@....com>,
	Will Deacon <Will.Deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	tglx@...utronix.de
Subject: Re: [PATCH 2/2] arm64: take onlined cpus into account when setting
 irq affinity in migrate_one_irq

On Wed, Aug 27, 2014 at 7:40 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>
>
> On 27/08/14 10:30, byungchul.park@....com wrote:
>>
>> From: Byungchul Park <byungchul.park@....com>
>>
>> This patch ensures that the cpu being offlined is not present in the
>> affinity mask.
>>
>
> I agree that this patch fixes the issue reported in [1] without
> disabling forced set affinity mask. However Thomas responded yesterday
> asking to disable it [2] on the original thread for ARM. I have
> responded on the thread and waiting for feedback from rmk and tglx. I
> would prefer to wait and align with ARM code if possible.

It is also good to call irq_set_affinity() with "force = false" to
solve the problem,
because it can give a chance to check if the passed affinity includes
only onlined cpus or not.
However, it totally relies on the implementation of irq_set_affinity(),
and it cannnot ensure that the function performs what we expect.
I think a code basically needs to be written to do exactly what it intends.

It is not bad to apply calling irq_set_affinity() with "force = false"
to the code if necessary.
But this patches also have to be applied, independently,
in order to make the code do exactly what it intends.

Thank you.

>
>> Signed-off-by: Byungchul Park <byungchul.park@....com>
>> ---
>>   arch/arm64/kernel/irq.c |    9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
>> index 473e5db..0c7b79e 100644
>> --- a/arch/arm64/kernel/irq.c
>> +++ b/arch/arm64/kernel/irq.c
>> @@ -87,6 +87,7 @@ static bool migrate_one_irq(struct irq_desc *desc)
>>   {
>>         struct irq_data *d = irq_desc_get_irq_data(desc);
>>         const struct cpumask *affinity = d->affinity;
>> +       struct cpumask tmp_affinity;
>>         struct irq_chip *c;
>>         bool ret = false;
>>
>> @@ -100,6 +101,14 @@ static bool migrate_one_irq(struct irq_desc *desc)
>>         if (cpumask_any_and(affinity, cpu_online_mask) >= nr_cpu_ids) {
>>                 affinity = cpu_online_mask;
>>                 ret = true;
>> +       } else {
>> +               /*
>> +                * when using forced irq_set_affinity we must ensure that
>> the cpu
>> +                * being offlined is not present in the affinity mask, it
>> may be
>> +                * selected as the target CPU otherwise
>> +                */
>> +               cpumask_and(&tmp_affinity, affinity, cpu_online_mask);
>
>
> In case we decide to retain forced set affinity, you can probably squash
> this cpumask_and with the above cpumask_any_and.
>
>> +               affinity = &tmp_affinity;
>>         }
>>
>>         c = irq_data_get_irq_chip(d);
>>
>
> Regards,
> Sudeep
>
> [1]
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/266785.html
> [2]
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-August/281548.html
>
> --
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LG electronics CTO division
senior engineer
max.byungchul.park
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