[PATCH 3/3] RFC: Solved unnecessary schedule latency in the TTY layer (3/3)
From: Ivo Sieben <hidden>
Date: 2012-05-03 12:38:06
Also in:
linux-serial
Subsystem:
the rest, tty layer and serial drivers · Maintainers:
Linus Torvalds, Greg Kroah-Hartman, Jiri Slaby
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 <redacted> --- 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