From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ivo Sieben Subject: [PATCH] RFC: Set irq thread to RT priority on creation Date: Thu, 30 May 2013 14:12:55 +0200 Message-ID: <1369915975-28797-1-git-send-email-meltedpianoman@gmail.com> Mime-Version: 1.0 Content-Type: text/plain Cc: LKML , Ivo Sieben To: RT , Thomas Gleixner , Sebastian Andrzej Siewior , Steven Rostedt Return-path: Received: from tx2ehsobe002.messaging.microsoft.com ([65.55.88.12]:7763 "EHLO tx2outboundpool.messaging.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753753Ab3E3MNP (ORCPT ); Thu, 30 May 2013 08:13:15 -0400 Sender: linux-rt-users-owner@vger.kernel.org List-ID: When a threaded irq handler is installed the irq thread is initially created on normal scheduling priority. Only after the the irq thread is woken up it sets its priority to RT_FIFO MAX_USER_RT_PRIO/2. 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 you would expect. Fixed this by setting the RT priority on creation of the irq_thread. Signed-off-by: Ivo Sieben --- RFC: Whas there a specific reason for the irq_thread to be created on normal scheduling and only set to RT priority when woken up? This patch solves an issue for me where a device driver is expected to handle an interrupt immediatly after irq handlers are installed and interrupts enabled. (If this does make sense: I guess the sched_setscheduler() call in the irq_thread function can be removed?) kernel/irq/manage.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index fa17855..0ffe37b 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -950,6 +950,9 @@ __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, new->name); @@ -957,6 +960,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new) ret = PTR_ERR(t); goto out_mput; } + + sched_setscheduler(t, SCHED_FIFO, ¶m); + /* * We keep the reference to the task struct even if * the thread dies to avoid that the interrupt code -- 1.7.9.5