[PATCH 2/3] RFC: Solved unnecessary schedule latency in the TTY layer (2/3)
From: Ivo Sieben <hidden>
Date: 2012-05-03 12:37:42
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 "normal" spin lock that guards the line discipline administration is replaced by a raw spin lock. 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> Conflicts: drivers/tty/tty_ldisc.c --- drivers/tty/tty_ldisc.c | 30 +++++++++++++++--------------- 1 files changed, 15 insertions(+), 15 deletions(-)
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 24b95db..30836cc 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c@@ -26,7 +26,7 @@ * callers who will do ldisc lookups and cannot sleep. */ -static DEFINE_SPINLOCK(tty_ldisc_lock); +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 */
@@ -53,18 +53,18 @@ static void put_ldisc(struct tty_ldisc *ld) * We really want an "atomic_dec_and_lock_irqsave()", * but we don't have it, so this does it by hand. */ - local_irq_save(flags); - if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) { + raw_spin_lock_irqsave(&tty_ldisc_lock, flags); + if (atomic_dec_and_test(&ld->users)) { struct tty_ldisc_ops *ldo = ld->ops; ldo->refcount--; module_put(ldo->owner); - spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); kfree(ld); return; } - local_irq_restore(flags); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); wake_up(&tty_ldisc_idle); }
@@ -89,11 +89,11 @@ int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc) if (disc < N_TTY || disc >= NR_LDISCS) return -EINVAL; - spin_lock_irqsave(&tty_ldisc_lock, flags); + raw_spin_lock_irqsave(&tty_ldisc_lock, flags); tty_ldiscs[disc] = new_ldisc; new_ldisc->num = disc; new_ldisc->refcount = 0; - spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); return ret; }
@@ -119,12 +119,12 @@ int tty_unregister_ldisc(int disc) if (disc < N_TTY || disc >= NR_LDISCS) return -EINVAL; - spin_lock_irqsave(&tty_ldisc_lock, flags); + raw_spin_lock_irqsave(&tty_ldisc_lock, flags); if (tty_ldiscs[disc]->refcount) ret = -EBUSY; else tty_ldiscs[disc] = NULL; - spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); return ret; }
@@ -135,7 +135,7 @@ static struct tty_ldisc_ops *get_ldops(int disc) unsigned long flags; struct tty_ldisc_ops *ldops, *ret; - spin_lock_irqsave(&tty_ldisc_lock, flags); + raw_spin_lock_irqsave(&tty_ldisc_lock, flags); ret = ERR_PTR(-EINVAL); ldops = tty_ldiscs[disc]; if (ldops) {
@@ -145,7 +145,7 @@ static struct tty_ldisc_ops *get_ldops(int disc) ret = ldops; } } - spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); return ret; }
@@ -153,10 +153,10 @@ static void put_ldops(struct tty_ldisc_ops *ldops) { unsigned long flags; - spin_lock_irqsave(&tty_ldisc_lock, flags); + raw_spin_lock_irqsave(&tty_ldisc_lock, flags); ldops->refcount--; module_put(ldops->owner); - spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); } /**
@@ -286,11 +286,11 @@ static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty) unsigned long flags; struct tty_ldisc *ld; - spin_lock_irqsave(&tty_ldisc_lock, flags); + raw_spin_lock_irqsave(&tty_ldisc_lock, flags); ld = NULL; if (test_bit(TTY_LDISC, &tty->flags)) ld = get_ldisc(tty->ldisc); - spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); return ld; }
--
1.7.0.4