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Date: Thu, 9 Jul 2009 23:49:46 +0800
From: Fengwei Yin <yfw.kernel@...il.com>
To: Alan Cox <alan@...rguk.ukuu.org.uk>
Cc: torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] tty: Sort out the USB sysrq changes that wrecked
performance
Hi Alan,
On Thu, Jul 9, 2009 at 8:35 PM, Alan Cox<alan@...rguk.ukuu.org.uk> wrote:
> 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);
>
What about the change like this:
diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index 932d624..b4fd33b 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -424,10 +424,26 @@ 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 {
+ /*
+ * Most of data shouldn't be sysrq request even when
+ * tty is a printk console.
+ */
+ if (time_before(jiffies, port->sysrq)) {
+ /* 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);
+ }
+ } else {
+ tty_insert_flip_string(tty, ch, urb->actual_length);
+ }
}
tty_flip_buffer_push(tty);
tty_kref_put(tty);
Regards
Yin, Fengwei
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