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SubjectRe: Schedule affinity_notify work while migrating IRQs during hot plug
On 2017-02-21 12:59, Sodagudi Prasad wrote:
> Hi Thomas,
>
> Currently irq_set_affinity() is called to migrate irqs from
> migrate_one_irq()
> during cpu hot plug and clients which are interested to know the irq
> affinity change
> not getting notified
>
> take_cpu_down () --> __cpu_disable() -->
> irq_migrate_all_off_this_cpu();
>
> irq_set_affinity() is changing the IRQ affinity at chip level
> but it is not notifying the affinity_notify work.
>

Hi Thomas and All,

I could see that in the 3.10 kernel irq affinity notifiers are getting
called when a core getting hot plugged. But in later kernel versions api
used to change
affinity was changed from irq_set_affinity_locked() to
irq_do_set_affinity(), so irq notifiers are not getting called when a
core hot plugged.
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/kernel/irq/manage.c?id=refs/tags/v3.10.105#n201


In latest kernel following path is executed to migrate IRQs.
irq_migrate_all_off_this_cpu() --> migrate_one_irq() ->
irq_do_set_affinity().

As I mentioned above, irq_set_affinity_locked() notifies all clients
drivers, which are registered for IRQ affinity change but
irq_do_set_affinity() API just changes the affinity at irq chip level
but does not notify the clients drivers. I am not sure whether it is
just a miss during IRQ framework refactor or intentionally done like
this. Can you please check whether following code change make sense or
not?

So I am thinking that, adding following sched_work() would notify
clients.

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 6b66959..5e4766b 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -207,6 +207,7 @@ int irq_do_set_affinity(struct irq_data *data, const
struct cpumask *mask,
case IRQ_SET_MASK_OK_DONE:
cpumask_copy(desc->irq_common_data.affinity, mask);
case IRQ_SET_MASK_OK_NOCOPY:
+ schedule_work(&desc->affinity_notify->work);
irq_set_thread_affinity(desc);
ret = 0;
}

> How about below change, so that clients drivers gets notified about
> irq affinity changes?
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -207,6 +207,7 @@ int irq_do_set_affinity(struct irq_data *data,
> const struct cpumask *mask,
> case IRQ_SET_MASK_OK_DONE:
> cpumask_copy(desc->irq_common_data.affinity, mask);
> case IRQ_SET_MASK_OK_NOCOPY:
> + schedule_work(&desc->affinity_notify->work);
> irq_set_thread_affinity(desc);
> ret = 0;
>
> With this change, notifications of IRQ affinity gets executed and
> notified
> to client drivers.

-Thanks, Prasad
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum,
Linux Foundation Collaborative Project

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