On 06/27/2013 09:59 PM, Jim Lin wrote: > On Fri, 2013-06-28 at 02:20 +0800, Stephen Warren wrote: >> 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. > In my case it takes about 95 ms on Tegra20 and Tegra114 for > usb_kbd_testc() to be called periodically. > So I set CONFIG_USBKB_TESTC_PERIOD to 100. > Like I said, if CONFIG_USBKB_TESTC_PERIOD ms < T < 1000 ms > we reduce polling (send command to USB keyboard to check is there > any key pressed) to every second.
OK, so I think how this works is: If nothing is happening, then usb_kbd_testc() is repeatedly called back-to-back with no delay between. So, if the time between two calls to usb_kbd_testc() is much longer than the time it takes to execute it once, then something else is going on, and hence the code should skip some calls to usb_kbd_testc(). If that's how this works, then why require CONFIG_USBKBD_TESTC_PERIOD to be set? Why not simply measure the time between when usb_kbd_testc() returns, and when it is re-entered? If it's very short, nothing else is happening. If it's very long, something else is happening. That is a far more direct measurement, and is immune to e.g. CPU frequency differences in a way that a static value for CONFIG_USBKBD_TESTC_PERIOD is not. Also, any kind of time measurement doesn't solve the issue I mentioned re: how granular the other task is. Finally, if you're sitting at the command-prompt, is usb_kbd_testc() used at all? How does regular typing using a USB keyboard interact with this code; will typing react fast, but CTRL-C react slowly? _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
