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Servers request TSC freq from kernel rather than each one measuring it individually

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This commit is contained in:
Erik van der Kouwe 2011-01-11 11:03:37 +00:00
parent 9b8f37bb27
commit 04229f0581
1 changed files with 24 additions and 58 deletions
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80
lib/libsys/tsc_util.c
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@ -10,7 +10,10 @@
#include "sysutil.h"
#define CALIBRATE_TICKS(h) ((h)/5)
#ifndef CONFIG_MAX_CPUS
#define CONFIG_MAX_CPUS 1
#endif
#define MICROHZ 1000000 /* number of micros per second */
#define MICROSPERTICK(h) (MICROHZ/(h)) /* number of micros per HZ tick */
@ -21,42 +24,28 @@
panic("calibrate failed: %d", r); \
}
static u32_t calib_tsc, Hz = 0;
static u32_t calib_mhz, Hz = 0;
static int calibrated = 0;
int
tsc_calibrate(void)
{
u64_t start, end, diff;
struct tms tms;
unsigned long t = 0;
struct cpu_info cpu_info[CONFIG_MAX_CPUS];
/* Get HZ. */
Hz = sys_hz();
/* Wait for clock to tick. */
while(!t || (t == times(&tms)))
t = times(&tms);
/* Obtain CPU frequency from kernel */
if (sys_getcpuinfo(&cpu_info)) {
printf("tsc_calibrate: cannot get cpu info\n");
return -1;
}
t++;
/* Wait for clock to tick CALIBRATE_TICKS times, and time
* this using the TSC.
/* For now, use the frequency of the first CPU; everything here will
* break down in case we get scheduled on multiple CPUs with different
* frequencies regardless
*/
read_tsc_64(&start);
while(times(&tms) < t+CALIBRATE_TICKS(Hz)) ;
read_tsc_64(&end);
diff = sub64(end, start);
if(ex64hi(diff) != 0)
panic("tsc_calibrate: CALIBRATE_TICKS too high for TSC frequency");
calib_tsc = ex64lo(diff);
#if 0
printf("tsc_calibrate: "
"%lu cycles/%d ticks of %d Hz; %lu cycles/s\n",
calib_tsc, CALIBRATE_TICKS(Hz), Hz,
div64u(mul64u(calib_tsc, Hz), CALIBRATE_TICKS(Hz)));
#endif
calib_mhz = cpu_info[0].freq;
calibrated = 1;
return OK;
@ -73,8 +62,7 @@ micro_delay(u32_t micros)
CALIBRATE;
/* We have to know when to end the delay. */
end = add64u(now, div64u(mul64u(calib_tsc,
micros * Hz / CALIBRATE_TICKS(Hz)), MICROHZ));
end = add64(now, mul64u(micros, calib_mhz * 1000));
/* If we have to wait for at least one HZ tick, use the regular
* tickdelay first. Round downwards on purpose, so the average
@ -95,38 +83,16 @@ micro_delay(u32_t micros)
u32_t tsc_64_to_micros(u64_t tsc)
{
u64_t tmp;
u32_t imv;
CALIBRATE;
/* Various formulas provide various levels of accuracy depending on
* what still fits in a 64-bit number.
*/
if (ex64hi(tsc) != 0) {
if (ex64hi(tsc) < ULONG_MAX) {
tmp = mul64u(ex64hi(tsc) + 1, MICROHZ);
if (ex64hi(tmp) == 0) {
imv = div64u(mul64(tsc, cvu64(MICROHZ)),
calib_tsc);
tmp = mul64u(imv, CALIBRATE_TICKS(Hz));
if (ex64hi(tmp) == 0) {
/* Mid accuracy. */
return ex64lo(tmp) / Hz;
}
}
}
/* Low accuracy for large numbers. */
return div64u(mul64u(div64u(tsc, calib_tsc),
MICROHZ * CALIBRATE_TICKS(Hz)), Hz);
tmp = div64u64(tsc, calib_mhz);
if (ex64hi(tmp)) {
printf("tsc_64_to_micros: more than 2^32ms\n");
return ~0UL;
} else {
return ex64lo(tmp);
}
/* High accuracy for small numbers (the common case). */
return div64u(mul64u(ex64lo(tsc), MICROHZ * CALIBRATE_TICKS(Hz)),
calib_tsc) / Hz;
}
u32_t tsc_to_micros(u32_t low, u32_t high)
@ -138,5 +104,5 @@ u32_t tsc_get_khz(void)
{
CALIBRATE;
return calib_tsc / (CALIBRATE_TICKS(Hz) * MICROSPERTICK(Hz)) * 1000;
return calib_mhz * 1000;
}