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Add random jitter to stat clock, the random jitter is +- 511 usec's, so 

we should average the nominal clock rate.

stathz now runs at hz (the hard clock hz), without getting high amounts of
time in interrupt handling.
This commit is contained in:
chris 2002-10-05 12:22:55 +00:00
parent c784454024
commit dfcb3e3552
1 changed files with 74 additions and 5 deletions
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79
sys/arch/arm/footbridge/footbridge_clock.c
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@ -1,4 +1,4 @@
/* $NetBSD: footbridge_clock.c,v 1.10 2002/10/02 05:02:30 thorpej Exp $ */
/* $NetBSD: footbridge_clock.c,v 1.11 2002/10/05 12:22:55 chris Exp $ */
/*
* Copyright (c) 1997 Mark Brinicombe.
@ -58,6 +58,18 @@ int clockhandler __P((void *));
int statclockhandler __P((void *));
static int load_timer __P((int, int));
/*
* Statistics clock variance, in usec. Variance must be a
* power of two. Since this gives us an even number, not an odd number,
* we discard one case and compensate. That is, a variance of 1024 would
* give us offsets in [0..1023]. Instead, we take offsets in [1..1023].
* This is symmetric about the point 512, or statvar/2, and thus averages
* to that value (assuming uniform random numbers).
*/
const int statvar = 1024;
int statmin; /* minimum stat clock count in ticks */
int statcountperusec; /* number of ticks per usec at current stathz */
int statprev; /* last value of we set statclock to */
#if 0
static int clockmatch __P((struct device *parent, struct cfdata *cf, void *aux));
@ -129,7 +141,6 @@ clockhandler(aframe)
return(0); /* Pass the interrupt on down the chain */
}
/*
* int statclockhandler(struct clockframe *frame)
*
@ -142,9 +153,51 @@ statclockhandler(aframe)
void *aframe;
{
struct clockframe *frame = aframe;
int newint, r;
int currentclock ;
/* start the clock off again */
bus_space_write_4(clock_sc->sc_iot, clock_sc->sc_ioh,
TIMER_2_CLEAR, 0);
TIMER_2_CLEAR, 0);
do {
r = random() & (statvar-1);
} while (r == 0);
newint = statmin + (r * statcountperusec);
/* fetch the current count */
currentclock = bus_space_read_4(clock_sc->sc_iot, clock_sc->sc_ioh,
TIMER_2_VALUE);
/*
* work out how much time has run, add another usec for time spent
* here
*/
r = ((statprev - currentclock) + statcountperusec);
if (r < newint) {
newint -= r;
r = 0;
}
else
printf("statclockhandler: Statclock overrun\n");
/*
* update the clock to the new counter, this reloads the existing
* timer
*/
bus_space_write_4(clock_sc->sc_iot, clock_sc->sc_ioh,
TIMER_2_LOAD, newint);
statprev = newint;
statclock(frame);
if (r)
/*
* We've completely overrun the previous interval,
* make sure we report the correct number of ticks.
*/
statclock(frame);
return(0); /* Pass the interrupt on down the chain */
}
@ -186,8 +239,24 @@ void
setstatclockrate(hz)
int hz;
{
int statint;
int countpersecond;
int statvarticks;
clock_sc->sc_statclock_count = load_timer(TIMER_2_BASE, hz);
/* statint == num in counter to drop by desired hz */
statint = clock_sc->sc_statclock_count = load_timer(TIMER_2_BASE, hz);
/* Get the total ticks a second */
countpersecond = statint * hz;
/* now work out how many ticks per usec */
statcountperusec = countpersecond / 1000000;
/* calculate a variance range of statvar */
statvarticks = statcountperusec * statvar;
/* minimum is statint - 50% of variant */
statmin = statint - (statvarticks / 2);
}
/*
@ -204,7 +273,7 @@ cpu_initclocks()
{
/* stathz and profhz should be set to something, we have the timer */
if (stathz == 0)
stathz = 64;
stathz = hz;
if (profhz == 0)
profhz = stathz * 5;