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Commit 3d3675cc authored by Roman Zippel's avatar Roman Zippel Committed by Linus Torvalds
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[PATCH] ntp: prescale time_offset 



This converts time_offset into a scaled per tick value.  This avoids now
completely the crude compensation in second_overflow().

Signed-off-by: default avatarRoman Zippel <zippel@linux-m68k.org>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent dc6a43e4

include/linux/timex.h

+1 −1
Original line number Diff line number Diff line
@@ -89,7 +89,7 @@ 
 * FINENSEC is 1 ns in SHIFT_UPDATE units of the time_phase variable.

 */

#define SHIFT_SCALE 22		/* phase scale (shift) */

#define SHIFT_UPDATE (SHIFT_KG + MAXTC) /* time offset scale (shift) */

#define SHIFT_UPDATE (SHIFT_HZ + 1) /* time offset scale (shift) */

#define SHIFT_USEC 16		/* frequency offset scale (shift) */

#define FINENSEC (1L << (SHIFT_SCALE - 10)) /* ~1 ns in phase units */

kernel/time/ntp.c

+16 −48
Original line number Diff line number Diff line
@@ -31,7 +31,7 @@ int tickadj = 500/HZ ? : 1; /* microsecs */ 
/* TIME_ERROR prevents overwriting the CMOS clock */

int time_state = TIME_OK;		/* clock synchronization status	*/

int time_status = STA_UNSYNC;		/* clock status bits		*/

long time_offset;			/* time adjustment (us)		*/

long time_offset;			/* time adjustment (ns)		*/

long time_constant = 2;			/* pll time constant		*/

long time_tolerance = MAXFREQ;		/* frequency tolerance (ppm)	*/

long time_precision = 1;		/* clock precision (us)		*/
@@ -57,6 +57,7 @@ void ntp_clear(void) 
	ntp_update_frequency();



	tick_length = tick_length_base;

	time_offset = 0;

}



#define CLOCK_TICK_OVERFLOW	(LATCH * HZ - CLOCK_TICK_RATE)
@@ -83,7 +84,7 @@ void ntp_update_frequency(void) 
 */

void second_overflow(void)

{

	long ltemp, time_adj;

	long time_adj;



	/* Bump the maxerror field */

	time_maxerror += time_tolerance >> SHIFT_USEC;
@@ -151,42 +152,14 @@ void second_overflow(void) 
	 * adjustment for each second is clamped so as to spread the adjustment

	 * over not more than the number of seconds between updates.

	 */

	ltemp = time_offset;

	if (!(time_status & STA_FLL))

		ltemp = shift_right(ltemp, SHIFT_KG + time_constant);

	ltemp = min(ltemp, (MAXPHASE / MINSEC) << SHIFT_UPDATE);

	ltemp = max(ltemp, -(MAXPHASE / MINSEC) << SHIFT_UPDATE);

	time_offset -= ltemp;

	time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);



	/*

	 * Compute the frequency estimate and additional phase adjustment due

	 * to frequency error for the next second.

	 */



#if HZ == 100

	/*

	 * Compensate for (HZ==100) != (1 << SHIFT_HZ).  Add 25% and 3.125% to

	 * get 128.125; => only 0.125% error (p. 14)

	 */

	time_adj += shift_right(time_adj, 2) + shift_right(time_adj, 5);

#endif

#if HZ == 250

	/*

	 * Compensate for (HZ==250) != (1 << SHIFT_HZ).  Add 1.5625% and

	 * 0.78125% to get 255.85938; => only 0.05% error (p. 14)

	 */

	time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);

#endif

#if HZ == 1000

	/*

	 * Compensate for (HZ==1000) != (1 << SHIFT_HZ).  Add 1.5625% and

	 * 0.78125% to get 1023.4375; => only 0.05% error (p. 14)

	 */

	time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);

#endif

	tick_length = tick_length_base;

	tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - (SHIFT_SCALE - 10));

	time_adj = time_offset;

	if (!(time_status & STA_FLL))

		time_adj = shift_right(time_adj, SHIFT_KG + time_constant);

	time_adj = min(time_adj, -((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);

	time_adj = max(time_adj, ((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);

	time_offset -= time_adj;

	tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);

}



/*
@@ -347,12 +320,8 @@ int do_adjtimex(struct timex *txc) 
		     * Scale the phase adjustment and

		     * clamp to the operating range.

		     */

		    if (ltemp > MAXPHASE)

		        time_offset = MAXPHASE << SHIFT_UPDATE;

		    else if (ltemp < -MAXPHASE)

			time_offset = -(MAXPHASE << SHIFT_UPDATE);

		    else

		        time_offset = ltemp << SHIFT_UPDATE;

		    time_offset = min(ltemp, MAXPHASE);

		    time_offset = max(time_offset, -MAXPHASE);



		    /*

		     * Select whether the frequency is to be controlled
@@ -366,8 +335,7 @@ int do_adjtimex(struct timex *txc) 
		    time_reftime = xtime.tv_sec;

		    if (time_status & STA_FLL) {

		        if (mtemp >= MINSEC) {

			    ltemp = (time_offset / mtemp) << (SHIFT_USEC -

							      SHIFT_UPDATE);

			    ltemp = ((time_offset << 12) / mtemp) << (SHIFT_USEC - 12);

			    time_freq += shift_right(ltemp, SHIFT_KH);

			} else /* calibration interval too short (p. 12) */

				result = TIME_ERROR;
@@ -382,6 +350,7 @@ int do_adjtimex(struct timex *txc) 
		    }

		    time_freq = min(time_freq, time_tolerance);

		    time_freq = max(time_freq, -time_tolerance);

		    time_offset = (time_offset * NSEC_PER_USEC / HZ) << SHIFT_UPDATE;

		} /* STA_PLL */

	    } /* txc->modes & ADJ_OFFSET */

	    if (txc->modes & ADJ_TICK)
@@ -395,9 +364,8 @@ leave: if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0) 


	if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)

	    txc->offset	   = save_adjust;

	else {

	    txc->offset = shift_right(time_offset, SHIFT_UPDATE);

	}

	else

	    txc->offset    = shift_right(time_offset, SHIFT_UPDATE) * HZ / 1000;

	txc->freq	   = time_freq;

	txc->maxerror	   = time_maxerror;

	txc->esterror	   = time_esterror;