* [PATCH] tty: Use raw spin lock to protect RX flip buffer
@ 2012-09-20 14:08 Ivo Sieben
2012-09-20 16:37 ` Alan Cox
0 siblings, 1 reply; 3+ messages in thread
From: Ivo Sieben @ 2012-09-20 14:08 UTC (permalink / raw)
To: Alan Cox, Greg KH, linux-serial, RT; +Cc: Ivo Sieben
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@gmail.com>
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] tty: Use raw spin lock to protect RX flip buffer
2012-09-20 14:08 [PATCH] tty: Use raw spin lock to protect RX flip buffer Ivo Sieben
@ 2012-09-20 16:37 ` Alan Cox
0 siblings, 0 replies; 3+ messages in thread
From: Alan Cox @ 2012-09-20 16:37 UTC (permalink / raw)
To: Ivo Sieben; +Cc: Greg KH, linux-serial, RT
On Thu, 20 Sep 2012 16:08:00 +0200
Ivo Sieben <meltedpianoman@gmail.com> wrote:
> The "normal" spin lock that guards the RX flip buffer is replaced by
> a raw spin lock.
Our current goal is to get the buffers into the tty_port structure so
we can try and get rid of some of the locks entirely. We have lockless
kfifos and the port lifetime is the device lifetime plus so hopefully
it'll go away entirely eventually.
In the meantime I've no real opinion on the spin/raw_spin choices as
it's basically an RT question not a tty one so if the rt folks are
happy with it so am I.
Alan
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH] tty: Use raw spin lock to protect RX flip buffer
@ 2012-09-24 9:24 Ivo Sieben
0 siblings, 0 replies; 3+ messages in thread
From: Ivo Sieben @ 2012-09-24 9:24 UTC (permalink / raw)
To: Thomas Gleixner, Steven Rostedt, Alan Cox, Greg KH, linux-serial,
RT
Cc: Ivo Sieben
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@gmail.com>
---
Repost
@Thomas Gleixner & Steven Rostedt:
Alan Cox has responded to this patch: "I've no real opinion on the spin/raw_spin
choices as it's basically an RT question not a tty one so if the rt folks are
happy with it so am I." Do you agree?
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2012-09-24 9:24 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
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2012-09-20 14:08 [PATCH] tty: Use raw spin lock to protect RX flip buffer Ivo Sieben
2012-09-20 16:37 ` Alan Cox
-- strict thread matches above, loose matches on Subject: below --
2012-09-24 9:24 Ivo Sieben
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