[U-Boot] [PATCH v3 1/2] console: usbkbd: Improve TFTP booting performance

[Stephen Warren <swarren@wwwdotorg.org>]

On 06/27/2013 03:45 AM, Jim Lin wrote:
> TFTP booting is observed a little bit slow, especially when a USB
> keyboard is installed.
> The fix is to move polling to every second if we sense that other task
> like TFTP boot is running.
> 

> diff --git a/common/usb_kbd.c b/common/usb_kbd.c

> +#ifdef CONFIG_USBKB_TESTC_PERIOD
> +	/*
> +	 * T is the time between two calls of usb_kbd_testc().
> +	 * If CONFIG_USBKB_TESTC_PERIOD ms < T < 1000 ms,
> +	 * it implies other task like TFTP boot is running,
> +	 * then we reduce polling to every second
> +	 * to improve TFTP booting performance.
> +	 */
> +	if ((get_timer(kbd_testc_tms) >=
> +	    (CONFIG_USBKB_TESTC_PERIOD * CONFIG_SYS_HZ / 1000)) &&
> +	    (get_timer(kbd_testc_tms) < CONFIG_SYS_HZ))
> +		return 0;
> +	else
> +		kbd_testc_tms = get_timer(0);
> +#endif

I have a hard time understanding why the fact that "some other task is
running" implies anything at all re: how often usb_kbd_testc() would be
called.

It's quite possible that "some other task" is extremely fine-grained,
and calls usb_kbd_testc() every 0.1ms, and would be severely negatively
affected by usb_kbd_testc() taking a long time to execute.

Conversly, it's quite possible that "some other task" is quite granular,
and calls usb_kbd_testc() a wide intervals, say every 200ms.

So, I think this change keys of entirely the wrong thing.

Shouldn't the TFTP process (or use of USB networking?) or other
long-running tasks that do check for keyboard IO simply set some flag to
indicate to usb_kbd_testc() that it should run at a reduced rate, or
even just have those long-running processses call usb_kbd_testc() at a
reduced rate themselves?