[tip:irq/core] genirq: Set irq thread to RT priority on creation

From: tip-bot for Ivo Sieben
Date: Wed Jun 12 2013 - 16:49:26 EST

Commit-ID: ee23871389d51e07380d23887333622fbe7d3dd9
Gitweb: http://git.kernel.org/tip/ee23871389d51e07380d23887333622fbe7d3dd9
Author: Ivo Sieben <meltedpianoman@xxxxxxxxx>
AuthorDate: Mon, 3 Jun 2013 12:12:02 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 11 Jun 2013 16:18:50 +0200

genirq: Set irq thread to RT priority on creation

When a threaded irq handler is installed the irq thread is initially
created on normal scheduling priority. Only after the irq thread is
woken up it sets its priority to RT_FIFO MAX_USER_RT_PRIO/2 itself.

This means that interrupts that occur directly after the irq handler
is installed will be handled on a normal scheduling priority instead
of the realtime priority that one would expect.

Fix this by setting the RT priority on creation of the irq_thread.

Signed-off-by: Ivo Sieben <meltedpianoman@xxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1370254322-17240-1-git-send-email-meltedpianoman@xxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
kernel/irq/manage.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index fa17855..e16caa8 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -840,9 +840,6 @@ static void irq_thread_dtor(struct callback_head *unused)
static int irq_thread(void *data)
struct callback_head on_exit_work;
- static const struct sched_param param = {
- .sched_priority = MAX_USER_RT_PRIO/2,
- };
struct irqaction *action = data;
struct irq_desc *desc = irq_to_desc(action->irq);
irqreturn_t (*handler_fn)(struct irq_desc *desc,
@@ -854,8 +851,6 @@ static int irq_thread(void *data)
handler_fn = irq_thread_fn;

- sched_setscheduler(current, SCHED_FIFO, &param);
init_task_work(&on_exit_work, irq_thread_dtor);
task_work_add(current, &on_exit_work, false);

@@ -950,6 +945,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
if (new->thread_fn && !nested) {
struct task_struct *t;
+ static const struct sched_param param = {
+ .sched_priority = MAX_USER_RT_PRIO/2,
+ };

t = kthread_create(irq_thread, new, "irq/%d-%s", irq,
@@ -957,6 +955,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
ret = PTR_ERR(t);
goto out_mput;
+ sched_setscheduler(t, SCHED_FIFO, &param);
* We keep the reference to the task struct even if
* the thread dies to avoid that the interrupt code
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