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Subject[PATCH v3 8/9] n_tty: Factor LNEXT processing from per-char i/o path
Date
LNEXT processing accounts for ~15% of total cpu time in end-to-end
tty i/o; factor the lnext test/clear from the per-char i/o path.

Instead, attempt to immediately handle the literal next char if not
at the end of this received buffer; otherwise, handle the first char
of the next received buffer as the literal next char, then continue
with normal i/o.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
drivers/tty/n_tty.c | 166 +++++++++++++++++++++++++++++-----------------------
1 file changed, 94 insertions(+), 72 deletions(-)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index f516247..d8cf96a 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -1248,9 +1248,11 @@ n_tty_receive_signal_char(struct tty_struct *tty, int signal, unsigned char c)
* caller holds non-exclusive termios_rwsem
* publishes canon_head if canonical mode is active
* otherwise, publishes read_head via put_tty_queue()
+ *
+ * Returns 1 if LNEXT was received, else returns 0
*/

-static void
+static int
n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
{
struct n_tty_data *ldata = tty->disc_data;
@@ -1260,24 +1262,24 @@ n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
if (c == START_CHAR(tty)) {
start_tty(tty);
commit_echoes(tty);
- return;
+ return 0;
}
if (c == STOP_CHAR(tty)) {
stop_tty(tty);
- return;
+ return 0;
}
}

if (L_ISIG(tty)) {
if (c == INTR_CHAR(tty)) {
n_tty_receive_signal_char(tty, SIGINT, c);
- return;
+ return 0;
} else if (c == QUIT_CHAR(tty)) {
n_tty_receive_signal_char(tty, SIGQUIT, c);
- return;
+ return 0;
} else if (c == SUSP_CHAR(tty)) {
n_tty_receive_signal_char(tty, SIGTSTP, c);
- return;
+ return 0;
}
}

@@ -1288,7 +1290,7 @@ n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)

if (c == '\r') {
if (I_IGNCR(tty))
- return;
+ return 0;
if (I_ICRNL(tty))
c = '\n';
} else if (c == '\n' && I_INLCR(tty))
@@ -1299,7 +1301,7 @@ n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
(c == WERASE_CHAR(tty) && L_IEXTEN(tty))) {
eraser(c, tty);
commit_echoes(tty);
- return;
+ return 0;
}
if (c == LNEXT_CHAR(tty) && L_IEXTEN(tty)) {
ldata->lnext = 1;
@@ -1311,10 +1313,9 @@ n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
commit_echoes(tty);
}
}
- return;
+ return 1;
}
- if (c == REPRINT_CHAR(tty) && L_ECHO(tty) &&
- L_IEXTEN(tty)) {
+ if (c == REPRINT_CHAR(tty) && L_ECHO(tty) && L_IEXTEN(tty)) {
size_t tail = ldata->canon_head;

finish_erasing(ldata);
@@ -1325,7 +1326,7 @@ n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
tail++;
}
commit_echoes(tty);
- return;
+ return 0;
}
if (c == '\n') {
if (L_ECHO(tty) || L_ECHONL(tty)) {
@@ -1366,7 +1367,7 @@ handle_newline:
kill_fasync(&tty->fasync, SIGIO, POLL_IN);
if (waitqueue_active(&tty->read_wait))
wake_up_interruptible(&tty->read_wait);
- return;
+ return 0;
}
}

@@ -1388,43 +1389,36 @@ handle_newline:
put_tty_queue(c, ldata);

put_tty_queue(c, ldata);
+ return 0;
}

-static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
+static inline void
+n_tty_receive_char_inline(struct tty_struct *tty, unsigned char c)
{
struct n_tty_data *ldata = tty->disc_data;
int parmrk;

- /*
- * If the previous character was LNEXT, or we know that this
- * character is not one of the characters that we'll have to
- * handle specially, do shortcut processing to speed things
- * up.
- */
- if (!test_bit(c, ldata->char_map) || ldata->lnext) {
- ldata->lnext = 0;
-
- if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
- I_IXANY(tty)) {
- start_tty(tty);
- process_echoes(tty);
- }
- if (L_ECHO(tty)) {
- finish_erasing(ldata);
- /* Record the column of first canon char. */
- if (ldata->canon_head == ldata->read_head)
- echo_set_canon_col(ldata);
- echo_char(c, tty);
- commit_echoes(tty);
- }
- parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
- if (parmrk)
- put_tty_queue(c, ldata);
- put_tty_queue(c, ldata);
- return;
+ if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
+ start_tty(tty);
+ process_echoes(tty);
}
+ if (L_ECHO(tty)) {
+ finish_erasing(ldata);
+ /* Record the column of first canon char. */
+ if (ldata->canon_head == ldata->read_head)
+ echo_set_canon_col(ldata);
+ echo_char(c, tty);
+ commit_echoes(tty);
+ }
+ parmrk = (c == (unsigned char) '\377' && I_PARMRK(tty)) ? 1 : 0;
+ if (parmrk)
+ put_tty_queue(c, ldata);
+ put_tty_queue(c, ldata);
+}

- n_tty_receive_char_special(tty, c);
+static inline void n_tty_receive_char(struct tty_struct *tty, unsigned char c)
+{
+ n_tty_receive_char_inline(tty, c);
}

static inline void
@@ -1432,33 +1426,19 @@ n_tty_receive_char_fast(struct tty_struct *tty, unsigned char c)
{
struct n_tty_data *ldata = tty->disc_data;

- /*
- * If the previous character was LNEXT, or we know that this
- * character is not one of the characters that we'll have to
- * handle specially, do shortcut processing to speed things
- * up.
- */
- if (!test_bit(c, ldata->char_map) || ldata->lnext) {
- ldata->lnext = 0;
-
- if (tty->stopped && !tty->flow_stopped && I_IXON(tty) &&
- I_IXANY(tty)) {
- start_tty(tty);
- process_echoes(tty);
- }
- if (L_ECHO(tty)) {
- finish_erasing(ldata);
- /* Record the column of first canon char. */
- if (ldata->canon_head == ldata->read_head)
- echo_set_canon_col(ldata);
- echo_char(c, tty);
- commit_echoes(tty);
- }
- put_tty_queue(c, ldata);
- return;
+ if (tty->stopped && !tty->flow_stopped && I_IXON(tty) && I_IXANY(tty)) {
+ start_tty(tty);
+ process_echoes(tty);
}
-
- n_tty_receive_char_special(tty, c);
+ if (L_ECHO(tty)) {
+ finish_erasing(ldata);
+ /* Record the column of first canon char. */
+ if (ldata->canon_head == ldata->read_head)
+ echo_set_canon_col(ldata);
+ echo_char(c, tty);
+ commit_echoes(tty);
+ }
+ put_tty_queue(c, ldata);
}

static inline void
@@ -1505,6 +1485,22 @@ n_tty_receive_char_flagged(struct tty_struct *tty, unsigned char c, char flag)
}
}

+static void
+n_tty_receive_char_lnext(struct tty_struct *tty, unsigned char c, char flag)
+{
+ struct n_tty_data *ldata = tty->disc_data;
+
+ ldata->lnext = 0;
+ if (likely(flag == TTY_NORMAL)) {
+ if (I_ISTRIP(tty))
+ c &= 0x7f;
+ if (I_IUCLC(tty) && L_IEXTEN(tty))
+ c = tolower(c);
+ n_tty_receive_char(tty, c);
+ } else
+ n_tty_receive_char_flagged(tty, c, flag);
+}
+
/**
* n_tty_receive_buf - data receive
* @tty: terminal device
@@ -1598,7 +1594,14 @@ n_tty_receive_buf_standard(struct tty_struct *tty, const unsigned char *cp,
put_tty_queue(c, ldata);
continue;
}
- n_tty_receive_char(tty, c);
+ if (!test_bit(c, ldata->char_map))
+ n_tty_receive_char_inline(tty, c);
+ else if (n_tty_receive_char_special(tty, c) && count) {
+ if (fp)
+ flag = *fp++;
+ n_tty_receive_char_lnext(tty, *cp++, flag);
+ count--;
+ }
} else
n_tty_receive_char_flagged(tty, *cp++, flag);
}
@@ -1608,14 +1611,24 @@ static void
n_tty_receive_buf_fast(struct tty_struct *tty, const unsigned char *cp,
char *fp, int count)
{
+ struct n_tty_data *ldata = tty->disc_data;
char flag = TTY_NORMAL;

while (count--) {
if (fp)
flag = *fp++;
- if (likely(flag == TTY_NORMAL))
- n_tty_receive_char_fast(tty, *cp++);
- else
+ if (likely(flag == TTY_NORMAL)) {
+ unsigned char c = *cp++;
+
+ if (!test_bit(c, ldata->char_map))
+ n_tty_receive_char_fast(tty, c);
+ else if (n_tty_receive_char_special(tty, c) && count) {
+ if (fp)
+ flag = *fp++;
+ n_tty_receive_char_lnext(tty, *cp++, flag);
+ count--;
+ }
+ } else
n_tty_receive_char_flagged(tty, *cp++, flag);
}
}
@@ -1633,6 +1646,15 @@ static void __receive_buf(struct tty_struct *tty, const unsigned char *cp,
else if (tty->closing && !L_EXTPROC(tty))
n_tty_receive_buf_closing(tty, cp, fp, count);
else {
+ if (ldata->lnext) {
+ char flag = TTY_NORMAL;
+
+ if (fp)
+ flag = *fp++;
+ n_tty_receive_char_lnext(tty, *cp++, flag);
+ count--;
+ }
+
if (!preops && !I_PARMRK(tty))
n_tty_receive_buf_fast(tty, cp, fp, count);
else
--
1.8.1.2


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