[PATCH] uio: eliminate extraneous irq thread under CONFIG_PREEMPT_RT

[Mike Schanne]

From 435db0a75de98d2021e02381a15a300137a544b3 Mon Sep 17 00:00:00 2001
From: Michael Schanne <mschanne@xxxxxxx>
Date: Wed, 5 Aug 2026 14:34:22 -0400
Subject: [PATCH] uio: eliminate extraneous irq thread under CONFIG_PREEMPT_RT

Commit f8a27dfa4b82d442af1c0645a5acc70cc97c67f6 ("uio: use threaded
interrupts") makes all uio interrupts threaded by default.  However
under CONFIG_PREEMPT_RT, all interrupts are already threaded.  This
results in 2 irq threads per uio instance, adding an unnecessary
extra context switch per interrupt.

Do not request a threaded interrupt for uio under CONFIG_PREEMPT_RT

Signed-off-by: Michael Schanne <mschanne@xxxxxxx>
---
 drivers/uio/uio.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 004a549c6..4e28777ac 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -448,8 +448,12 @@ static irqreturn_t uio_interrupt_handler(int irq, void *dev_id)
        irqreturn_t ret;

        ret = idev->info->handler(irq, idev->info);
-       if (ret == IRQ_HANDLED)
-               ret = IRQ_WAKE_THREAD;
+       if (ret == IRQ_HANDLED) {
+               if (IS_ENABLED(CONFIG_PREEMPT_RT))
+                       uio_event_notify(idev->info);
+               else
+                       ret = IRQ_WAKE_THREAD;
+       }

        return ret;
 }
@@ -1038,8 +1042,13 @@ int __uio_register_device(struct module *owner,
                 * FDs at the time of unregister and therefore may not be
                 * freed until they are released.
                 */
-               ret = request_threaded_irq(info->irq, uio_interrupt_handler, uio_interrupt_thread,
-                                          info->irq_flags, info->name, idev);
+               if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+                       ret = request_irq(info->irq, uio_interrupt_handler,
+                               info->irq_flags, info->name, idev);
+               } else {
+                       ret = request_threaded_irq(info->irq, uio_interrupt_handler, uio_interrupt_thread,
+                               info->irq_flags, info->name, idev);
+               }
                if (ret) {
                        info->uio_dev = NULL;
                        goto err_request_irq;
--
2.34.1

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