On Thu, May 03, 2012 at 02:37:43PM +0200, Ivo Sieben wrote:
> 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.
This patch makes sense even in a non-RT case, as it localizes the lock
to the specific ldisc.
Alan, any objection to me applying this one to the tree now?
thanks,
greg k-h
> 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
>
>
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