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Reduce hardclock() code path length wrt/ multiply/divide by

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re-calculating the th_scale value only when necessary.
As discussed with gdamore@. Tested at (sub-)usec level with
stratum 1 reference.
This commit is contained in:
kardel 2006-09-24 06:39:28 +00:00
parent c57f7f2cdb
commit 182632b893
1 changed files with 12 additions and 8 deletions
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20
sys/kern/kern_tc.c
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@ -1,4 +1,4 @@
/* $NetBSD: kern_tc.c,v 1.12 2006/09/10 08:09:46 tsutsui Exp $ */
/* $NetBSD: kern_tc.c,v 1.13 2006/09/24 06:39:28 kardel Exp $ */
/*-
* ----------------------------------------------------------------------------
@ -11,7 +11,7 @@
#include <sys/cdefs.h>
/* __FBSDID("$FreeBSD: src/sys/kern/kern_tc.c,v 1.166 2005/09/19 22:16:31 andre Exp $"); */
__KERNEL_RCSID(0, "$NetBSD: kern_tc.c,v 1.12 2006/09/10 08:09:46 tsutsui Exp $");
__KERNEL_RCSID(0, "$NetBSD: kern_tc.c,v 1.13 2006/09/24 06:39:28 kardel Exp $");
#include "opt_ntp.h"
@ -518,9 +518,10 @@ tc_windup(void)
struct timehands *th, *tho;
u_int64_t scale;
u_int delta, ncount, ogen;
int i;
int i, s_update;
time_t t;
s_update = 0;
/*
* Make the next timehands a copy of the current one, but do not
* overwrite the generation or next pointer. While we update
@ -576,6 +577,7 @@ tc_windup(void)
for (; i > 0; i--) {
t = bt.sec;
ntp_update_second(&th->th_adjustment, &bt.sec);
s_update = 1;
if (bt.sec != t)
timebasebin.sec += bt.sec - t;
}
@ -589,6 +591,7 @@ tc_windup(void)
if (th->th_counter != timecounter) {
th->th_counter = timecounter;
th->th_offset_count = ncount;
s_update = 1;
printf("timecounter: selected timecounter \"%s\" frequency %ju Hz quality %d\n",
timecounter->tc_name, (uintmax_t)timecounter->tc_frequency,
@ -618,11 +621,12 @@ tc_windup(void)
* to the goddess of code clarity.
*
*/
scale = (u_int64_t)1 << 63;
scale += (th->th_adjustment / 1024) * 2199;
scale /= th->th_counter->tc_frequency;
th->th_scale = scale * 2;
if (s_update) {
scale = (u_int64_t)1 << 63;
scale += (th->th_adjustment / 1024) * 2199;
scale /= th->th_counter->tc_frequency;
th->th_scale = scale * 2;
}
/*
* Now that the struct timehands is again consistent, set the new
* generation number, making sure to not make it zero.