Solved unnecessary schedule latency in the TTY layer when used in
realtime context:
The global wait_queue that is used for line discipline idle handling is
moved to a separate wait_queue for each line instance. This prevents
unnecessary blocking on one line, because of idle handling on another
line.
Note: In a PREEMPT_RT system "normal" spin locks behave like mutexes and
no interrupts (and therefor no scheduling) is disabled.
Signed-off-by: Ivo Sieben <meltedpianoman@xxxxxxxxx>
---
drivers/tty/tty_ldisc.c | 7 ++++---
include/linux/tty_ldisc.h | 2 ++
2 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 30836cc..77eb299 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -28,7 +28,6 @@
static DEFINE_RAW_SPINLOCK(tty_ldisc_lock);
static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait);
-static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_idle);
/* Line disc dispatch table */
static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
@@ -65,7 +64,7 @@ static void put_ldisc(struct tty_ldisc *ld)
return;
}
raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
- wake_up(&tty_ldisc_idle);
+ wake_up(&ld->wq_idle);
}
/**
@@ -200,6 +199,8 @@ static struct tty_ldisc *tty_ldisc_get(int disc)
ld->ops = ldops;
atomic_set(&ld->users, 1);
+ init_waitqueue_head(&ld->wq_idle);
+
return ld;
}
@@ -538,7 +539,7 @@ static void tty_ldisc_flush_works(struct tty_struct *tty)
static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout)
{
long ret;
- ret = wait_event_timeout(tty_ldisc_idle,
+ ret = wait_event_timeout(tty->ldisc->wq_idle,
atomic_read(&tty->ldisc->users) == 1, timeout);
return ret > 0 ? 0 : -EBUSY;
}
diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h
index ff7dc08..fb79dd8 100644
--- a/include/linux/tty_ldisc.h
+++ b/include/linux/tty_ldisc.h
@@ -110,6 +110,7 @@
#include <linux/fs.h>
#include <linux/wait.h>
#include <linux/pps_kernel.h>
+#include <linux/wait.h>
struct tty_ldisc_ops {
int magic;
@@ -154,6 +155,7 @@ struct tty_ldisc_ops {
struct tty_ldisc {
struct tty_ldisc_ops *ops;
atomic_t users;
+ wait_queue_head_t wq_idle;
};
#define TTY_LDISC_MAGIC 0x5403
--
1.7.0.4
--
To unsubscribe from this list: send the line "unsubscribe linux-serial" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
