Commit 074b3b87 authored by Roman Zippel's avatar Roman Zippel Committed by Linus Torvalds
Browse files

ntp: increase time_freq resolution 



This changes time_freq to a 64bit value and makes it static (the only outside
user had no real need to modify it).  Intermediate values were already 64bit,
so the change isn't that big, but it saves a little in shifts by replacing
SHIFT_NSEC with TICK_LENGTH_SHIFT.  PPM_SCALE is then used to convert between
user space and kernel space representation.

Signed-off-by: default avatarRoman Zippel <zippel@linux-m68k.org>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent eea83d89

arch/powerpc/kernel/time.c

+0 −2
Original line number Diff line number Diff line
@@ -1007,8 +1007,6 @@ void __init time_init(void) 
	vdso_data->stamp_xsec = (u64) xtime.tv_sec * XSEC_PER_SEC;

	vdso_data->tb_to_xs = tb_to_xs;



	time_freq = 0;



	write_sequnlock_irqrestore(&xtime_lock, flags);



	/* Register the clocksource, if we're not running on iSeries */

include/linux/timex.h

+6 −5
Original line number Diff line number Diff line
@@ -86,11 +86,14 @@ 
 */

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

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

#define SHIFT_NSEC 12		/* kernel frequency offset scale */

#define PPM_SCALE (NSEC_PER_USEC << (TICK_LENGTH_SHIFT - SHIFT_USEC))

#define PPM_SCALE_INV_SHIFT 20

#define PPM_SCALE_INV ((1ll << (PPM_SCALE_INV_SHIFT + TICK_LENGTH_SHIFT)) / \

		       PPM_SCALE + 1)



#define MAXPHASE 512000L        /* max phase error (us) */

#define MAXFREQ (512L << SHIFT_USEC)  /* max frequency error (ppm) */

#define MAXFREQ_NSEC (512000L << SHIFT_NSEC) /* max frequency error (ppb) */

#define MAXFREQ 500000		/* max frequency error (ns/s) */

#define MAXFREQ_SCALED ((s64)MAXFREQ << TICK_LENGTH_SHIFT)

#define MINSEC 256		/* min interval between updates (s) */

#define MAXSEC 2048		/* max interval between updates (s) */

#define	NTP_PHASE_LIMIT	(MAXPHASE << 5)	/* beyond max. dispersion */
@@ -209,8 +212,6 @@ extern int time_status; /* clock synchronization status bits */ 
extern long time_maxerror;	/* maximum error */

extern long time_esterror;	/* estimated error */



extern long time_freq;		/* frequency offset (scaled ppm) */



extern long time_adjust;	/* The amount of adjtime left */



extern void ntp_clear(void);

kernel/time/ntp.c

+15 −15
Original line number Diff line number Diff line
@@ -39,7 +39,7 @@ static s64 time_offset; /* time adjustment (ns) */ 
static long time_constant = 2;		/* pll time constant		*/

long time_maxerror = NTP_PHASE_LIMIT;	/* maximum error (us)		*/

long time_esterror = NTP_PHASE_LIMIT;	/* estimated error (us)		*/

long time_freq;				/* frequency offset (scaled ppm)*/

static s64 time_freq;			/* frequency offset (scaled ns/s)*/

static long time_reftime;		/* time at last adjustment (s)	*/

long time_adjust;

static long ntp_tick_adj;
@@ -49,7 +49,7 @@ static void ntp_update_frequency(void) 
	u64 second_length = (u64)(tick_usec * NSEC_PER_USEC * USER_HZ)

				<< TICK_LENGTH_SHIFT;

	second_length += (s64)ntp_tick_adj << TICK_LENGTH_SHIFT;

	second_length += (s64)time_freq << (TICK_LENGTH_SHIFT - SHIFT_NSEC);

	second_length += time_freq;



	tick_length_base = second_length;
@@ -86,16 +86,16 @@ static void ntp_update_offset(long offset) 
	time_reftime = xtime.tv_sec;



	freq_adj = time_offset * mtemp;

	freq_adj = shift_right(freq_adj, time_constant * 2 +

			   (SHIFT_PLL + 2) * 2 - SHIFT_NSEC);

	freq_adj <<= TICK_LENGTH_SHIFT - 2 * (SHIFT_PLL + 2 + time_constant);

	time_status &= ~STA_MODE;

	if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {

		freq_adj += div_s64(time_offset << (SHIFT_NSEC - SHIFT_FLL), mtemp);

		freq_adj += div_s64(time_offset << (TICK_LENGTH_SHIFT - SHIFT_FLL),

				    mtemp);

		time_status |= STA_MODE;

	}

	freq_adj += time_freq;

	freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);

	time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);

	freq_adj = min(freq_adj, MAXFREQ_SCALED);

	time_freq = max(freq_adj, -MAXFREQ_SCALED);

	time_offset = div_s64(time_offset, NTP_INTERVAL_FREQ);

	time_offset <<= SHIFT_UPDATE;

}
@@ -131,7 +131,7 @@ void second_overflow(void) 
	long time_adj;



	/* Bump the maxerror field */

	time_maxerror += MAXFREQ >> SHIFT_USEC;

	time_maxerror += MAXFREQ / NSEC_PER_USEC;

	if (time_maxerror > NTP_PHASE_LIMIT) {

		time_maxerror = NTP_PHASE_LIMIT;

		time_status |= STA_UNSYNC;
@@ -323,10 +323,9 @@ int do_adjtimex(struct timex *txc) 
			time_status &= ~STA_NANO;



		if (txc->modes & ADJ_FREQUENCY) {

			time_freq = min(txc->freq, MAXFREQ);

			time_freq = min(time_freq, -MAXFREQ);

			time_freq = ((s64)time_freq * NSEC_PER_USEC)

					>> (SHIFT_USEC - SHIFT_NSEC);

			time_freq = (s64)txc->freq * PPM_SCALE;

			time_freq = min(time_freq, MAXFREQ_SCALED);

			time_freq = max(time_freq, -MAXFREQ_SCALED);

		}



		if (txc->modes & ADJ_MAXERROR)
@@ -369,14 +368,15 @@ int do_adjtimex(struct timex *txc) 
		if (!(time_status & STA_NANO))

			txc->offset /= NSEC_PER_USEC;

	}

	txc->freq	   = (time_freq / NSEC_PER_USEC) <<

				(SHIFT_USEC - SHIFT_NSEC);

	txc->freq	   = shift_right((s32)(time_freq >> PPM_SCALE_INV_SHIFT) *

					 (s64)PPM_SCALE_INV,

					 TICK_LENGTH_SHIFT);

	txc->maxerror	   = time_maxerror;

	txc->esterror	   = time_esterror;

	txc->status	   = time_status;

	txc->constant	   = time_constant;

	txc->precision	   = 1;

	txc->tolerance	   = MAXFREQ;

	txc->tolerance	   = MAXFREQ_SCALED / PPM_SCALE;

	txc->tick	   = tick_usec;



	/* PPS is not implemented, so these are zero */

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