linux-kernel - [PATCH 1/3] tty: Sort out the USB sysrq changes that wrecked performance

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Date:	Thu, 09 Jul 2009 13:35:52 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] tty: Sort out the USB sysrq changes that wrecked
	performance

From: Alan Cox <alan@...ux.intel.com>

We can't go around calling all sorts of magic per character functions at
full rate 3G data speed.

Signed-off-by: Alan Cox <alan@...ux.intel.com>
---

 drivers/usb/serial/generic.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)


diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index 932d624..e9aa7a4 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -424,10 +424,17 @@ static void flush_and_resubmit_read_urb(struct usb_serial_port *port)
 	if (!tty)
 		goto done;
 
-	/* Push data to tty */
-	for (i = 0; i < urb->actual_length; i++, ch++) {
-		if (!usb_serial_handle_sysrq_char(port, *ch))
-			tty_insert_flip_char(tty, *ch, TTY_NORMAL);
+	/* The per character mucking around with sysrq path it too slow for
+	   stuff like 3G modems, so shortcircuit it in the 99.9999999% of cases
+	   where the USB serial is not a console anyway */	
+	if (!port->console || !port->sysrq)
+		tty_insert_flip_string(tty, ch, urb->actual_length);
+	else {	
+		/* Push data to tty */
+		for (i = 0; i < urb->actual_length; i++, ch++) {
+			if (!usb_serial_handle_sysrq_char(port, *ch))
+				tty_insert_flip_char(tty, *ch, TTY_NORMAL);
+		}
 	}
 	tty_flip_buffer_push(tty);
 	tty_kref_put(tty);

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