From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 11 Nov 2011 07:10:42 +0000 (+0100)
Subject: Merge branch 'formingo/3.2/tip/timers/core' of git://git.linaro.org/people/jstultz... 
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=367177e50189ab0a983b52f3d3f7eb2a1927db71;p=linux-beck.git

Merge branch 'formingo/3.2/tip/timers/core' of git://git.linaro.org/people/jstultz/linux into timers/core

Conflicts:
	kernel/time/timekeeping.c
---

367177e50189ab0a983b52f3d3f7eb2a1927db71
diff --cc kernel/time/timekeeping.c
index 025e136f3881,e65ff3171102..e9f60d311436
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@@ -847,58 -817,16 +847,65 @@@ static void timekeeping_adjust(s64 offs
  			offset = -offset;
  		} else
  			adj = timekeeping_bigadjust(error, &interval, &offset);
 -	} else
 +	} else /* No adjustment needed */
  		return;
  
+ 	WARN_ONCE(timekeeper.clock->maxadj &&
+ 			(timekeeper.mult + adj > timekeeper.clock->mult +
+ 						timekeeper.clock->maxadj),
+ 			"Adjusting %s more then 11%% (%ld vs %ld)\n",
+ 			timekeeper.clock->name, (long)timekeeper.mult + adj,
+ 			(long)timekeeper.clock->mult +
+ 				timekeeper.clock->maxadj);
 +	/*
 +	 * So the following can be confusing.
 +	 *
 +	 * To keep things simple, lets assume adj == 1 for now.
 +	 *
 +	 * When adj != 1, remember that the interval and offset values
 +	 * have been appropriately scaled so the math is the same.
 +	 *
 +	 * The basic idea here is that we're increasing the multiplier
 +	 * by one, this causes the xtime_interval to be incremented by
 +	 * one cycle_interval. This is because:
 +	 *	xtime_interval = cycle_interval * mult
 +	 * So if mult is being incremented by one:
 +	 *	xtime_interval = cycle_interval * (mult + 1)
 +	 * Its the same as:
 +	 *	xtime_interval = (cycle_interval * mult) + cycle_interval
 +	 * Which can be shortened to:
 +	 *	xtime_interval += cycle_interval
 +	 *
 +	 * So offset stores the non-accumulated cycles. Thus the current
 +	 * time (in shifted nanoseconds) is:
 +	 *	now = (offset * adj) + xtime_nsec
 +	 * Now, even though we're adjusting the clock frequency, we have
 +	 * to keep time consistent. In other words, we can't jump back
 +	 * in time, and we also want to avoid jumping forward in time.
 +	 *
 +	 * So given the same offset value, we need the time to be the same
 +	 * both before and after the freq adjustment.
 +	 *	now = (offset * adj_1) + xtime_nsec_1
 +	 *	now = (offset * adj_2) + xtime_nsec_2
 +	 * So:
 +	 *	(offset * adj_1) + xtime_nsec_1 =
 +	 *		(offset * adj_2) + xtime_nsec_2
 +	 * And we know:
 +	 *	adj_2 = adj_1 + 1
 +	 * So:
 +	 *	(offset * adj_1) + xtime_nsec_1 =
 +	 *		(offset * (adj_1+1)) + xtime_nsec_2
 +	 *	(offset * adj_1) + xtime_nsec_1 =
 +	 *		(offset * adj_1) + offset + xtime_nsec_2
 +	 * Canceling the sides:
 +	 *	xtime_nsec_1 = offset + xtime_nsec_2
 +	 * Which gives us:
 +	 *	xtime_nsec_2 = xtime_nsec_1 - offset
 +	 * Which simplfies to:
 +	 *	xtime_nsec -= offset
 +	 *
 +	 * XXX - TODO: Doc ntp_error calculation.
 +	 */
  	timekeeper.mult += adj;
  	timekeeper.xtime_interval += interval;
  	timekeeper.xtime_nsec -= offset;