Messages in this thread Patch in this message | | | Date | Tue, 4 Jun 2013 20:28:30 +0200 | From | Andreas Mohr <> | Subject | [PATCH] usbnet: improve/fix status interrupt endpoint interval |
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From 307685fe8e6dfc8181e30167b9c31479332cb22f Mon Sep 17 00:00:00 2001 From: Andreas Mohr <andim2@users.sourceforge.net> Date: Sun, 2 Jun 2013 20:37:05 +0200 Subject: [PATCH] usbnet: improve/fix status interrupt endpoint interval tweaking.
- failed to take super-speed into account - <= full-speed seems to have wrong value (specified as frames [ms], thus 3 is not suitable to achieve 8ms) Value 8 now managed to reduce powertop wakeups from ~ 540 to ~ 155 - add detailed docs and question marks about current practice --- drivers/net/usb/usbnet.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
Found this with MCS7830 on a full-speed USB 1.1 port (Inspiron 8000). Good to have a rusty notebook with noisy PSU coils, else it would have taken a lot longer to nail it ;) Tested on -rc4, checkpath.pl:d.
Signed-off-by: Andreas Mohr <andim2@users.sourceforge.net>
diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c index 06ee82f..b6e9569 100644 --- a/drivers/net/usb/usbnet.c +++ b/drivers/net/usb/usbnet.c @@ -231,8 +231,23 @@ static int init_status (struct usbnet *dev, struct usb_interface *intf) maxp = usb_maxpacket (dev->udev, pipe, 0); /* avoid 1 msec chatter: min 8 msec poll rate */ + /* High/SuperSpeed expresses intervals in microframes + * (in logarithmic encoding, PRIOR to encoding in URB) + * rather than frames. + * Thus, for >= HighSpeed: == X [microframes] * 125us [-> 8ms], + * <= FullSpeed: == X [ms] [-> 8ms]. + * Finally, it's questionable whether we'll even get away unscathed + * with doing such rate tweaking at all: + * bInterval value is declared as being a hard demand by a device + * in order to guarantee having its I/O needs serviced properly... + * if we don't do this, then... [overruns], [fire], [apocalypse]? + * If this turns out to be problematic, such policy should be moved + * to individual drivers (indicate flag to [dis]allow rate tweaking + * as tolerated by specific devices). + */ period = max ((int) dev->status->desc.bInterval, - (dev->udev->speed == USB_SPEED_HIGH) ? 7 : 3); + ((dev->udev->speed == USB_SPEED_HIGH) || + (dev->udev->speed == USB_SPEED_SUPER)) ? 7 : 8); buf = kmalloc (maxp, GFP_KERNEL); if (buf) { -- 1.7.10.4
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