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From: Nicholas Piggin <npiggin@gmail.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: Nicholas Piggin <npiggin@gmail.com>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH 11/15] tty: hvc: hvc_poll break hv read loop
Date: Tue,  1 May 2018 00:55:54 +1000	[thread overview]
Message-ID: <20180430145558.4308-12-npiggin@gmail.com> (raw)
In-Reply-To: <20180430145558.4308-1-npiggin@gmail.com>

Avoid looping with the spinlock held while there is read data
being returned from the hv driver. Instead note if the entire
size returned by tty_buffer_request_room was read, and request
another read poll.

This limits the critical section lengths, and provides more
even service to other consoles in case there is a pathological
condition.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 drivers/tty/hvc/hvc_console.c | 88 ++++++++++++++++++-----------------
 1 file changed, 45 insertions(+), 43 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index fddb63322c67..745ac220fce8 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -592,7 +592,7 @@ static u32 timeout = MIN_TIMEOUT;
 int hvc_poll(struct hvc_struct *hp)
 {
 	struct tty_struct *tty;
-	int i, n, poll_mask = 0;
+	int i, n, count, poll_mask = 0;
 	char buf[N_INBUF] __ALIGNED__;
 	unsigned long flags;
 	int read_total = 0;
@@ -618,7 +618,7 @@ int hvc_poll(struct hvc_struct *hp)
 
 	/* Now check if we can get data (are we throttled ?) */
 	if (tty_throttled(tty))
-		goto throttled;
+		goto out;
 
 	/* If we aren't notifier driven and aren't throttled, we always
 	 * request a reschedule
@@ -627,56 +627,58 @@ int hvc_poll(struct hvc_struct *hp)
 		poll_mask |= HVC_POLL_READ;
 
 	/* Read data if any */
-	for (;;) {
-		int count = tty_buffer_request_room(&hp->port, N_INBUF);
 
-		/* If flip is full, just reschedule a later read */
-		if (count == 0) {
+	count = tty_buffer_request_room(&hp->port, N_INBUF);
+
+	/* If flip is full, just reschedule a later read */
+	if (count == 0) {
+		poll_mask |= HVC_POLL_READ;
+		goto out;
+	}
+
+	n = hp->ops->get_chars(hp->vtermno, buf, count);
+	if (n <= 0) {
+		/* Hangup the tty when disconnected from host */
+		if (n == -EPIPE) {
+			spin_unlock_irqrestore(&hp->lock, flags);
+			tty_hangup(tty);
+			spin_lock_irqsave(&hp->lock, flags);
+		} else if ( n == -EAGAIN ) {
+			/*
+			 * Some back-ends can only ensure a certain min
+			 * num of bytes read, which may be > 'count'.
+			 * Let the tty clear the flip buff to make room.
+			 */
 			poll_mask |= HVC_POLL_READ;
-			break;
 		}
+		goto out;
+	}
 
-		n = hp->ops->get_chars(hp->vtermno, buf, count);
-		if (n <= 0) {
-			/* Hangup the tty when disconnected from host */
-			if (n == -EPIPE) {
-				spin_unlock_irqrestore(&hp->lock, flags);
-				tty_hangup(tty);
-				spin_lock_irqsave(&hp->lock, flags);
-			} else if ( n == -EAGAIN ) {
-				/*
-				 * Some back-ends can only ensure a certain min
-				 * num of bytes read, which may be > 'count'.
-				 * Let the tty clear the flip buff to make room.
-				 */
-				poll_mask |= HVC_POLL_READ;
-			}
-			break;
-		}
-		for (i = 0; i < n; ++i) {
+	for (i = 0; i < n; ++i) {
 #ifdef CONFIG_MAGIC_SYSRQ
-			if (hp->index == hvc_console.index) {
-				/* Handle the SysRq Hack */
-				/* XXX should support a sequence */
-				if (buf[i] == '\x0f') {	/* ^O */
-					/* if ^O is pressed again, reset
-					 * sysrq_pressed and flip ^O char */
-					sysrq_pressed = !sysrq_pressed;
-					if (sysrq_pressed)
-						continue;
-				} else if (sysrq_pressed) {
-					handle_sysrq(buf[i]);
-					sysrq_pressed = 0;
+		if (hp->index == hvc_console.index) {
+			/* Handle the SysRq Hack */
+			/* XXX should support a sequence */
+			if (buf[i] == '\x0f') {	/* ^O */
+				/* if ^O is pressed again, reset
+				 * sysrq_pressed and flip ^O char */
+				sysrq_pressed = !sysrq_pressed;
+				if (sysrq_pressed)
 					continue;
-				}
+			} else if (sysrq_pressed) {
+				handle_sysrq(buf[i]);
+				sysrq_pressed = 0;
+				continue;
 			}
-#endif /* CONFIG_MAGIC_SYSRQ */
-			tty_insert_flip_char(&hp->port, buf[i], 0);
 		}
-
-		read_total += n;
+#endif /* CONFIG_MAGIC_SYSRQ */
+		tty_insert_flip_char(&hp->port, buf[i], 0);
 	}
- throttled:
+	if (n == count)
+		poll_mask |= HVC_POLL_READ;
+	read_total = n;
+
+ out:
 	/* Wakeup write queue if necessary */
 	if (hp->do_wakeup) {
 		hp->do_wakeup = 0;
-- 
2.17.0

  parent reply	other threads:[~2018-04-30 14:55 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-30 14:55 [PATCH 00/15] hvc and powerpc opal console latency reduction Nicholas Piggin
2018-04-30 14:55 ` [PATCH 01/15] powerpc/powernv: opal_put_chars partial write fix Nicholas Piggin
2018-07-24 13:59   ` [01/15] " Michael Ellerman
2018-04-30 14:55 ` [PATCH 02/15] powerpc/powernv: Fix OPAL console driver OPAL_BUSY loops Nicholas Piggin
2018-04-30 14:55 ` [PATCH 03/15] powerpc/powernv: opal-kmsg standardise OPAL_BUSY handling Nicholas Piggin
2018-04-30 14:55 ` [PATCH 04/15] powerpc/powernv: opal-kmsg use flush fallback from console code Nicholas Piggin
2018-05-04  5:16   ` Michael Ellerman
2018-05-04  5:37     ` Nicholas Piggin
2018-05-07 10:36       ` Michael Ellerman
2018-05-08  3:40         ` Nicholas Piggin
2018-04-30 14:55 ` [PATCH 05/15] powerpc/powernv: Implement and use opal_flush_console Nicholas Piggin
2018-04-30 14:55 ` [PATCH 06/15] powerpc/powernv: Remove OPALv1 support from opal console driver Nicholas Piggin
2018-04-30 14:55 ` [PATCH 07/15] powerpc/powernv: move opal console flushing to udbg Nicholas Piggin
2018-04-30 14:55 ` [PATCH 08/15] powerpc/powernv: implement opal_put_chars_atomic Nicholas Piggin
2018-05-01  9:48   ` Benjamin Herrenschmidt
2018-05-01 10:37     ` Nicholas Piggin
2018-05-07 10:35       ` Michael Ellerman
2018-05-08  3:36         ` Nicholas Piggin
2018-04-30 14:55 ` [PATCH 09/15] tty: hvc: remove unexplained "just in case" spin delay Nicholas Piggin
2018-04-30 14:55 ` [PATCH 10/15] tty: hvc: use mutex instead of spinlock for hvc_structs lock Nicholas Piggin
2018-08-13 11:22   ` [10/15] " Michael Ellerman
2018-04-30 14:55 ` Nicholas Piggin [this message]
2018-08-13 11:23   ` [11/15] tty: hvc: hvc_poll break hv read loop Michael Ellerman
2018-04-30 14:55 ` [PATCH 12/15] tty: hvc: hvc_poll may sleep Nicholas Piggin
2018-08-13 11:23   ` [12/15] " Michael Ellerman
2018-04-30 14:55 ` [PATCH 13/15] tty: hvc: hvc_write " Nicholas Piggin
2018-08-13 11:23   ` [13/15] " Michael Ellerman
2018-04-30 14:55 ` [PATCH 14/15] tty: hvc: introduce the hv_ops.flush operation for hvc drivers Nicholas Piggin
2018-08-13 11:23   ` [14/15] " Michael Ellerman
2018-04-30 14:55 ` [PATCH 15/15] powerpc/powernv: provide a console flush operation for opal hvc driver Nicholas Piggin
2018-08-21 10:35   ` [15/15] " Michael Ellerman

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