The "normal" spin lock that guards the RX flip buffer is replaced by a raw
spin lock.
On a PREEMP_RT system this prevents unwanted scheduling overhead when data is
read at the same time as data is being received: while RX IRQ threaded handling
is busy a TTY read call is performed from a RT priority > threaded IRQ priority.
The read call tries to take the flip buffer spin lock (held by the threaded IRQ)
which blocks and causes a context switch to/from the threaded IRQ handler until
the spin lock is unlocked.
On a 240 MHz AT91SAM9261 processor setup this fixes about 100us of scheduling
overhead on the TTY read call.
Signed-off-by: Ivo Sieben <meltedpianoman@xxxxxxxxx>
---
drivers/tty/tty_buffer.c | 44 ++++++++++++++++++++++----------------------
include/linux/kbd_kern.h | 4 ++--
include/linux/tty.h | 2 +-
3 files changed, 25 insertions(+), 25 deletions(-)
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index b8e90b8..fd4c242 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -135,20 +135,20 @@ static void __tty_buffer_flush(struct tty_struct *tty)
void tty_buffer_flush(struct tty_struct *tty)
{
unsigned long flags;
- spin_lock_irqsave(&tty->buf.lock, flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, flags);
/* If the data is being pushed to the tty layer then we can't
process it here. Instead set a flag and the flush_to_ldisc
path will process the flush request before it exits */
if (test_bit(TTY_FLUSHING, &tty->flags)) {
set_bit(TTY_FLUSHPENDING, &tty->flags);
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
wait_event(tty->read_wait,
test_bit(TTY_FLUSHPENDING, &tty->flags) == 0);
return;
} else
__tty_buffer_flush(tty);
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
}
/**
@@ -238,9 +238,9 @@ int tty_buffer_request_room(struct tty_struct *tty, size_t size)
unsigned long flags;
int length;
- spin_lock_irqsave(&tty->buf.lock, flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, flags);
length = __tty_buffer_request_room(tty, size);
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
return length;
}
EXPORT_SYMBOL_GPL(tty_buffer_request_room);
@@ -268,18 +268,18 @@ int tty_insert_flip_string_fixed_flag(struct tty_struct *tty,
unsigned long flags;
struct tty_buffer *tb;
- spin_lock_irqsave(&tty->buf.lock, flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, flags);
space = __tty_buffer_request_room(tty, goal);
tb = tty->buf.tail;
/* If there is no space then tb may be NULL */
if (unlikely(space == 0)) {
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
break;
}
memcpy(tb->char_buf_ptr + tb->used, chars, space);
memset(tb->flag_buf_ptr + tb->used, flag, space);
tb->used += space;
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
copied += space;
chars += space;
/* There is a small chance that we need to split the data over
@@ -313,18 +313,18 @@ int tty_insert_flip_string_flags(struct tty_struct *tty,
unsigned long __flags;
struct tty_buffer *tb;
- spin_lock_irqsave(&tty->buf.lock, __flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, __flags);
space = __tty_buffer_request_room(tty, goal);
tb = tty->buf.tail;
/* If there is no space then tb may be NULL */
if (unlikely(space == 0)) {
- spin_unlock_irqrestore(&tty->buf.lock, __flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, __flags);
break;
}
memcpy(tb->char_buf_ptr + tb->used, chars, space);
memcpy(tb->flag_buf_ptr + tb->used, flags, space);
tb->used += space;
- spin_unlock_irqrestore(&tty->buf.lock, __flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, __flags);
copied += space;
chars += space;
flags += space;
@@ -357,7 +357,7 @@ int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
unsigned long flags;
struct tty_buffer *tb;
- spin_lock_irqsave(&tty->buf.lock, flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, flags);
space = __tty_buffer_request_room(tty, size);
tb = tty->buf.tail;
@@ -366,7 +366,7 @@ int tty_prepare_flip_string(struct tty_struct *tty, unsigned char **chars,
memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
tb->used += space;
}
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
return space;
}
EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
@@ -394,7 +394,7 @@ int tty_prepare_flip_string_flags(struct tty_struct *tty,
unsigned long __flags;
struct tty_buffer *tb;
- spin_lock_irqsave(&tty->buf.lock, __flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, __flags);
space = __tty_buffer_request_room(tty, size);
tb = tty->buf.tail;
@@ -403,7 +403,7 @@ int tty_prepare_flip_string_flags(struct tty_struct *tty,
*flags = tb->flag_buf_ptr + tb->used;
tb->used += space;
}
- spin_unlock_irqrestore(&tty->buf.lock, __flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, __flags);
return space;
}
EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
@@ -433,7 +433,7 @@ static void flush_to_ldisc(struct work_struct *work)
if (disc == NULL) /* !TTY_LDISC */
return;
- spin_lock_irqsave(&tty->buf.lock, flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, flags);
if (!test_and_set_bit(TTY_FLUSHING, &tty->flags)) {
struct tty_buffer *head;
@@ -462,10 +462,10 @@ static void flush_to_ldisc(struct work_struct *work)
char_buf = head->char_buf_ptr + head->read;
flag_buf = head->flag_buf_ptr + head->read;
head->read += count;
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
disc->ops->receive_buf(tty, char_buf,
flag_buf, count);
- spin_lock_irqsave(&tty->buf.lock, flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, flags);
}
clear_bit(TTY_FLUSHING, &tty->flags);
}
@@ -477,7 +477,7 @@ static void flush_to_ldisc(struct work_struct *work)
clear_bit(TTY_FLUSHPENDING, &tty->flags);
wake_up(&tty->read_wait);
}
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
tty_ldisc_deref(disc);
}
@@ -519,10 +519,10 @@ void tty_flush_to_ldisc(struct tty_struct *tty)
void tty_flip_buffer_push(struct tty_struct *tty)
{
unsigned long flags;
- spin_lock_irqsave(&tty->buf.lock, flags);
+ raw_spin_lock_irqsave(&tty->buf.lock, flags);
if (tty->buf.tail != NULL)
tty->buf.tail->commit = tty->buf.tail->used;
- spin_unlock_irqrestore(&tty->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&tty->buf.lock, flags);
if (tty->low_latency)
flush_to_ldisc(&tty->buf.work);
@@ -543,7 +543,7 @@ EXPORT_SYMBOL(tty_flip_buffer_push);
void tty_buffer_init(struct tty_struct *tty)
{
- spin_lock_init(&tty->buf.lock);
+ raw_spin_lock_init(&tty->buf.lock);
tty->buf.head = NULL;
tty->buf.tail = NULL;
tty->buf.free = NULL;
diff --git a/include/linux/kbd_kern.h b/include/linux/kbd_kern.h
index daf4a3a..507af24 100644
--- a/include/linux/kbd_kern.h
+++ b/include/linux/kbd_kern.h
@@ -150,10 +150,10 @@ extern unsigned int keymap_count;
static inline void con_schedule_flip(struct tty_struct *t)
{
unsigned long flags;
- spin_lock_irqsave(&t->buf.lock, flags);
+ raw_spin_lock_irqsave(&t->buf.lock, flags);
if (t->buf.tail != NULL)
t->buf.tail->commit = t->buf.tail->used;
- spin_unlock_irqrestore(&t->buf.lock, flags);
+ raw_spin_unlock_irqrestore(&t->buf.lock, flags);
schedule_work(&t->buf.work);
}
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 9f47ab5..e728ecc 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -86,7 +86,7 @@ struct tty_buffer {
struct tty_bufhead {
struct work_struct work;
- spinlock_t lock;
+ raw_spinlock_t lock;
struct tty_buffer *head; /* Queue head */
struct tty_buffer *tail; /* Active buffer */
struct tty_buffer *free; /* Free queue head */
--
1.7.9.5
--
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