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Subject[PATCH 2/3] usb-serial: regression fix to move sysrq from hot path
Date
A performance regression was introduced by commit:
98fcb5f78165b8a3d93870ad7afd4d9ebbb8b43a

The sysrq handling should only get executed if the attached usb serial
device is acting as a serial system console. A serial system console
has a very low input throughput vs a 3g usb modem which pushes bytes
through the same interface at a high rate.

Entire strings of output can be processed via the tty input when the
device is not a console.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
drivers/usb/serial/generic.c | 16 ++++++++++++----
1 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index 932d624..82b8883 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -425,11 +425,19 @@ static void flush_and_resubmit_read_urb(struct usb_serial_port *port)
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);
+ if (port->console) {
+ 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);
+ } else if (urb->actual_length) {
+ i = tty_buffer_request_room(tty, urb->actual_length);
+ if (i) {
+ tty_insert_flip_string(tty, urb->transfer_buffer, i);
+ tty_flip_buffer_push(tty);
+ }
}
- tty_flip_buffer_push(tty);
tty_kref_put(tty);
done:
usb_serial_generic_resubmit_read_urb(port, GFP_ATOMIC);
--
1.6.3.1.9.g95405b


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