USB: Patch to align the various USB timers to fire at the same time

This patch modifies the USB regular 250ms timer to be "perfectly aligned" to
the second and quarters thereof. This change is there to make sure that if
you have multiple USB ports, the timers for all these ports will fire at the
same time rather than all spread out. All spread out wakes the CPU up from
power saving idle a lot more than needed...


Signed-off-by: Arjan van de Ven <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/core/hcd.c

···
 	}
 
 	/* The USB 2.0 spec says 256 ms.  This is close enough and won't
-	 * exceed that limit if HZ is 100. */
+	 * exceed that limit if HZ is 100. The math is more clunky than
+	 * maybe expected, this is to make sure that all timers for USB devices
+	 * fire at the same time to give the CPU a break inbetween */
 	if (hcd->uses_new_polling ? hcd->poll_rh :
 			(length == 0 && hcd->status_urb != NULL))
-		mod_timer (&hcd->rh_timer, jiffies + msecs_to_jiffies(250));
+		mod_timer (&hcd->rh_timer, (jiffies/(HZ/4) + 1) * (HZ/4));
 }
 EXPORT_SYMBOL_GPL(usb_hcd_poll_rh_status);
 
···
 		urb->hcpriv = hcd;	/* indicate it's queued */
 
 		if (!hcd->uses_new_polling)
-			mod_timer (&hcd->rh_timer, jiffies +
-					msecs_to_jiffies(250));
+			mod_timer (&hcd->rh_timer,
+				(jiffies/(HZ/4) + 1) * (HZ/4));
 
 		/* If a status change has already occurred, report it ASAP */
 		else if (hcd->poll_pending)