On Mon, Aug 17, 2020 at 07:53:55PM +0530, Sumit Garg wrote:

On Mon, 17 Aug 2020 at 19:27, Doug Anderson [off-list ref] wrote:

quoted

Hi,

On Mon, Aug 17, 2020 at 5:27 AM Sumit Garg [off-list ref] wrote:

quoted

Thanks for your suggestion, irq_work_schedule() looked even better
without any overhead, see below:

diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index 3082378..1eade89 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h

@@ -3,6 +3,7 @@
 #define _LINUX_IRQ_WORK_H

 #include <linux/smp_types.h>
+#include <linux/workqueue.h>

 /*
  * An entry can be in one of four states:

@@ -24,6 +25,11 @@ struct irq_work {
        void (*func)(struct irq_work *);
 };

+struct irq_work_schedule {
+       struct irq_work work;
+       struct work_struct *sched_work;
+};
+
 static inline
 void init_irq_work(struct irq_work *work, void (*func)(struct irq_work *))
 {
 {

@@ -39,6 +45,7 @@ void init_irq_work(struct irq_work *work, void

(*func)(struct irq_work *))

 bool irq_work_queue(struct irq_work *work);
 bool irq_work_queue_on(struct irq_work *work, int cpu);
+bool irq_work_schedule(struct work_struct *sched_work);

 void irq_work_tick(void);
 void irq_work_sync(struct irq_work *work);

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index eca8396..3880316 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c

@@ -24,6 +24,8 @@
 static DEFINE_PER_CPU(struct llist_head, raised_list);
 static DEFINE_PER_CPU(struct llist_head, lazy_list);

+static struct irq_work_schedule irq_work_sched;
+
 /*
  * Claim the entry so that no one else will poke at it.
  */

@@ -79,6 +81,25 @@ bool irq_work_queue(struct irq_work *work)
 }
 EXPORT_SYMBOL_GPL(irq_work_queue);

+static void irq_work_schedule_fn(struct irq_work *work)
+{
+       struct irq_work_schedule *irq_work_sched =
+               container_of(work, struct irq_work_schedule, work);
+
+       if (irq_work_sched->sched_work)
+               schedule_work(irq_work_sched->sched_work);
+}
+
+/* Schedule work via irq work queue */
+bool irq_work_schedule(struct work_struct *sched_work)
+{
+       init_irq_work(&irq_work_sched.work, irq_work_schedule_fn);
+       irq_work_sched.sched_work = sched_work;
+
+       return irq_work_queue(&irq_work_sched.work);
+}
+EXPORT_SYMBOL_GPL(irq_work_schedule);

Wait, howzat work?  There's a single global variable that you stash
the "sched_work" into with no locking?  What if two people schedule
work at the same time?

This API is intended to be invoked from NMI context only, so I think
there will be a single user at a time.

How can you possibly know that?

This is library code, not a helper in a driver.


Daniel.

And we can make that explicit
as well:

+/* Schedule work via irq work queue */
+bool irq_work_schedule(struct work_struct *sched_work)
+{
+       if (in_nmi()) {
+               init_irq_work(&irq_work_sched.work, irq_work_schedule_fn);
+               irq_work_sched.sched_work = sched_work;
+
+               return irq_work_queue(&irq_work_sched.work);
+       }
+
+       return false;
+}
+EXPORT_SYMBOL_GPL(irq_work_schedule);

-Sumit

quoted

-Doug

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel