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tty: Use raw spin lock to protect TTY ldisc administration 

The global "normal" spin lock that guards the line discipline
administration is replaced by a raw spin lock. On a PREEMPT_RT system this
prevents unwanted scheduling overhead around the line discipline administration.

On a 200 MHz AT91SAM9261 processor setup this fixes about 100us of scheduling
overhead on a TTY read or write call.

Signed-off-by: Ivo Sieben <meltedpianoman@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ivo Sieben 2012-10-17 14:03:14 +02:00 committed by Greg Kroah-Hartman
parent ad3d1e5fc9
commit c97399418a
1 changed files with 16 additions and 16 deletions
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32
drivers/tty/tty_ldisc.c
View File

@ -26,7 +26,7 @@
* callers who will do ldisc lookups and cannot sleep. * 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_wait);
/* Line disc dispatch table */ /* Line disc dispatch table */
static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS]; static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS];
@ -49,21 +49,21 @@ static void put_ldisc(struct tty_ldisc *ld)
* If this is the last user, free the ldisc, and * If this is the last user, free the ldisc, and
* release the ldisc ops. * release the ldisc ops.
* *
* We really want an "atomic_dec_and_lock_irqsave()", * We really want an "atomic_dec_and_raw_lock_irqsave()",
* but we don't have it, so this does it by hand. * but we don't have it, so this does it by hand.
*/ */
local_irq_save(flags); raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
if (atomic_dec_and_lock(&ld->users, &tty_ldisc_lock)) { if (atomic_dec_and_test(&ld->users)) {
struct tty_ldisc_ops *ldo = ld->ops; struct tty_ldisc_ops *ldo = ld->ops;
ldo->refcount--; ldo->refcount--;
module_put(ldo->owner); module_put(ldo->owner);
spin_unlock_irqrestore(&tty_ldisc_lock, flags); raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
kfree(ld); kfree(ld);
return; return;
} }
local_irq_restore(flags); raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
wake_up(&ld->wq_idle); wake_up(&ld->wq_idle);
} }
@ -88,11 +88,11 @@ int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc)
if (disc < N_TTY || disc >= NR_LDISCS) if (disc < N_TTY || disc >= NR_LDISCS)
return -EINVAL; return -EINVAL;
spin_lock_irqsave(&tty_ldisc_lock, flags); raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
tty_ldiscs[disc] = new_ldisc; tty_ldiscs[disc] = new_ldisc;
new_ldisc->num = disc; new_ldisc->num = disc;
new_ldisc->refcount = 0; new_ldisc->refcount = 0;
spin_unlock_irqrestore(&tty_ldisc_lock, flags); raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret; return ret;
} }
@ -118,12 +118,12 @@ int tty_unregister_ldisc(int disc)
if (disc < N_TTY || disc >= NR_LDISCS) if (disc < N_TTY || disc >= NR_LDISCS)
return -EINVAL; return -EINVAL;
spin_lock_irqsave(&tty_ldisc_lock, flags); raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
if (tty_ldiscs[disc]->refcount) if (tty_ldiscs[disc]->refcount)
ret = -EBUSY; ret = -EBUSY;
else else
tty_ldiscs[disc] = NULL; tty_ldiscs[disc] = NULL;
spin_unlock_irqrestore(&tty_ldisc_lock, flags); raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret; return ret;
} }
@ -134,7 +134,7 @@ static struct tty_ldisc_ops *get_ldops(int disc)
unsigned long flags; unsigned long flags;
struct tty_ldisc_ops *ldops, *ret; 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); ret = ERR_PTR(-EINVAL);
ldops = tty_ldiscs[disc]; ldops = tty_ldiscs[disc];
if (ldops) { if (ldops) {
@ -144,7 +144,7 @@ static struct tty_ldisc_ops *get_ldops(int disc)
ret = ldops; ret = ldops;
} }
} }
spin_unlock_irqrestore(&tty_ldisc_lock, flags); raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret; return ret;
} }
@ -152,10 +152,10 @@ static void put_ldops(struct tty_ldisc_ops *ldops)
{ {
unsigned long flags; unsigned long flags;
spin_lock_irqsave(&tty_ldisc_lock, flags); raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
ldops->refcount--; ldops->refcount--;
module_put(ldops->owner); module_put(ldops->owner);
spin_unlock_irqrestore(&tty_ldisc_lock, flags); raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
} }
/** /**
@ -287,11 +287,11 @@ static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty)
unsigned long flags; unsigned long flags;
struct tty_ldisc *ld; struct tty_ldisc *ld;
spin_lock_irqsave(&tty_ldisc_lock, flags); raw_spin_lock_irqsave(&tty_ldisc_lock, flags);
ld = NULL; ld = NULL;
if (test_bit(TTY_LDISC, &tty->flags)) if (test_bit(TTY_LDISC, &tty->flags))
ld = get_ldisc(tty->ldisc); ld = get_ldisc(tty->ldisc);
spin_unlock_irqrestore(&tty_ldisc_lock, flags); raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ld; return ld;
} }