The "normal" spin lock that guards the N_TTY line discipline read section
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 read section 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/n_tty.c | 44 ++++++++++++++++++++++----------------------
drivers/tty/tty_io.c | 2 +-
include/linux/tty.h | 2 +-
3 files changed, 24 insertions(+), 24 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index ee1c268..743ef45 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -138,9 +138,9 @@ static void put_tty_queue(unsigned char c, struct tty_struct *tty)
* The problem of stomping on the buffers ends here.
* Why didn't anyone see this one coming? --AJK
*/
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
put_tty_queue_nolock(c, tty);
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
}
/**
@@ -173,9 +173,9 @@ static void reset_buffer_flags(struct tty_struct *tty)
{
unsigned long flags;
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
tty->read_head = tty->read_tail = tty->read_cnt = 0;
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
mutex_lock(&tty->echo_lock);
tty->echo_pos = tty->echo_cnt = tty->echo_overrun = 0;
@@ -230,7 +230,7 @@ static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
unsigned long flags;
ssize_t n = 0;
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
if (!tty->icanon) {
n = tty->read_cnt;
} else if (tty->canon_data) {
@@ -238,7 +238,7 @@ static ssize_t n_tty_chars_in_buffer(struct tty_struct *tty)
tty->canon_head - tty->read_tail :
tty->canon_head + (N_TTY_BUF_SIZE - tty->read_tail);
}
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
return n;
}
@@ -868,19 +868,19 @@ static void eraser(unsigned char c, struct tty_struct *tty)
kill_type = WERASE;
else {
if (!L_ECHO(tty)) {
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
tty->read_cnt -= ((tty->read_head - tty->canon_head) &
(N_TTY_BUF_SIZE - 1));
tty->read_head = tty->canon_head;
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
return;
}
if (!L_ECHOK(tty) || !L_ECHOKE(tty) || !L_ECHOE(tty)) {
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
tty->read_cnt -= ((tty->read_head - tty->canon_head) &
(N_TTY_BUF_SIZE - 1));
tty->read_head = tty->canon_head;
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
finish_erasing(tty);
echo_char(KILL_CHAR(tty), tty);
/* Add a newline if ECHOK is on and ECHOKE is off. */
@@ -914,10 +914,10 @@ static void eraser(unsigned char c, struct tty_struct *tty)
break;
}
cnt = (tty->read_head - head) & (N_TTY_BUF_SIZE-1);
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
tty->read_head = head;
tty->read_cnt -= cnt;
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
if (L_ECHO(tty)) {
if (L_ECHOPRT(tty)) {
if (!tty->erasing) {
@@ -1290,12 +1290,12 @@ send_signal:
put_tty_queue(c, tty);
handle_newline:
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
set_bit(tty->read_head, tty->read_flags);
put_tty_queue_nolock(c, tty);
tty->canon_head = tty->read_head;
tty->canon_data++;
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
kill_fasync(&tty->fasync, SIGIO, POLL_IN);
if (waitqueue_active(&tty->read_wait))
wake_up_interruptible(&tty->read_wait);
@@ -1371,7 +1371,7 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
return;
if (tty->real_raw) {
- spin_lock_irqsave(&tty->read_lock, cpuflags);
+ raw_spin_lock_irqsave(&tty->read_lock, cpuflags);
i = min(N_TTY_BUF_SIZE - tty->read_cnt,
N_TTY_BUF_SIZE - tty->read_head);
i = min(count, i);
@@ -1387,7 +1387,7 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp,
memcpy(tty->read_buf + tty->read_head, cp, i);
tty->read_head = (tty->read_head + i) & (N_TTY_BUF_SIZE-1);
tty->read_cnt += i;
- spin_unlock_irqrestore(&tty->read_lock, cpuflags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, cpuflags);
} else {
for (i = count, p = cp, f = fp; i; i--, p++) {
if (f)
@@ -1633,23 +1633,23 @@ static int copy_from_read_buf(struct tty_struct *tty,
bool is_eof;
retval = 0;
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
n = min(tty->read_cnt, N_TTY_BUF_SIZE - tty->read_tail);
n = min(*nr, n);
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
if (n) {
retval = copy_to_user(*b, &tty->read_buf[tty->read_tail], n);
n -= retval;
is_eof = n == 1 &&
tty->read_buf[tty->read_tail] == EOF_CHAR(tty);
tty_audit_add_data(tty, &tty->read_buf[tty->read_tail], n);
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
tty->read_tail = (tty->read_tail + n) & (N_TTY_BUF_SIZE-1);
tty->read_cnt -= n;
/* Turn single EOF into zero-length read */
if (L_EXTPROC(tty) && tty->icanon && is_eof && !tty->read_cnt)
n = 0;
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
*b += n;
*nr -= n;
}
@@ -1838,7 +1838,7 @@ do_it_again:
eol = test_and_clear_bit(tty->read_tail,
tty->read_flags);
c = tty->read_buf[tty->read_tail];
- spin_lock_irqsave(&tty->read_lock, flags);
+ raw_spin_lock_irqsave(&tty->read_lock, flags);
tty->read_tail = ((tty->read_tail+1) &
(N_TTY_BUF_SIZE-1));
tty->read_cnt--;
@@ -1850,7 +1850,7 @@ do_it_again:
if (--tty->canon_data < 0)
tty->canon_data = 0;
}
- spin_unlock_irqrestore(&tty->read_lock, flags);
+ raw_spin_unlock_irqrestore(&tty->read_lock, flags);
if (!eol || (c != __DISABLED_CHAR)) {
if (tty_put_user(tty, c, b++)) {
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index b425c79..a3ef00b 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2943,7 +2943,7 @@ void initialize_tty_struct(struct tty_struct *tty,
mutex_init(&tty->atomic_write_lock);
mutex_init(&tty->output_lock);
mutex_init(&tty->echo_lock);
- spin_lock_init(&tty->read_lock);
+ raw_spin_lock_init(&tty->read_lock);
spin_lock_init(&tty->ctrl_lock);
INIT_LIST_HEAD(&tty->tty_files);
INIT_WORK(&tty->SAK_work, do_SAK_work);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index e728ecc..21bceef 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -327,7 +327,7 @@ struct tty_struct {
struct mutex echo_lock;
unsigned char *write_buf;
int write_cnt;
- spinlock_t read_lock;
+ raw_spinlock_t read_lock;
/* If the tty has a pending do_SAK, queue it here - akpm */
struct work_struct SAK_work;
struct tty_port *port;
--
1.7.9.5
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