Re: Schedule affinity_notify work while migrating IRQs during hot plug

[Sodagudi Prasad]

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
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