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

[Fengwei Yin]

Hi Alan,

On Thu, Jul 9, 2009 at 8:35 PM, Alan Cox<alan@xxxxxxxxxxxxxxxxxxx> wrote:
> From: Alan Cox <alan@xxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx>
> ---
>
>  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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