diff options
author | Nate Lawson <njl@FreeBSD.org> | 2005-02-05 23:16:27 +0000 |
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committer | Nate Lawson <njl@FreeBSD.org> | 2005-02-05 23:16:27 +0000 |
commit | 959c26396c1335efde43ade9982fab9bb9c72d8b (patch) | |
tree | 0e1f039adcdea95909bcd77418b2001d569179ae /sys/amd64 | |
parent | 76ce4cc4565caa2f0ad658462bd00021f1a51cb4 (diff) | |
download | src-959c26396c1335efde43ade9982fab9bb9c72d8b.tar.gz src-959c26396c1335efde43ade9982fab9bb9c72d8b.zip |
Make cpu_est_clockrate() more accurate by disabling interrupts for the
millisecond it is calibrating. Suggested by jhb@ and bde@. Don't clobber
the tsc_freq with the new value since it isn't accurate enough for
timecounters and the timecounter system as a whole needs support for
changing rates before we do this. Subtract 0.5% from our measurement
to account for overhead in DELAY. Note that this interface is for
estimating the clockrate and needs to work well at runtime so doing a full
calibration including disabling interrupts for a second is not feasible.
Notes
Notes:
svn path=/head/; revision=141374
Diffstat (limited to 'sys/amd64')
-rw-r--r-- | sys/amd64/amd64/machdep.c | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/sys/amd64/amd64/machdep.c b/sys/amd64/amd64/machdep.c index 527c61bd1dbb..422c0fb949d2 100644 --- a/sys/amd64/amd64/machdep.c +++ b/sys/amd64/amd64/machdep.c @@ -456,6 +456,7 @@ cpu_boot(int howto) int cpu_est_clockrate(int cpu_id, uint64_t *rate) { + register_t reg; uint64_t tsc1, tsc2; if (pcpu_find(cpu_id) == NULL || rate == NULL) @@ -475,9 +476,11 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate) #endif /* Calibrate by measuring a short delay. */ + reg = intr_disable(); tsc1 = rdtsc(); DELAY(1000); tsc2 = rdtsc(); + intr_restore(reg); #ifdef SMP mtx_lock_spin(&sched_lock); @@ -485,8 +488,13 @@ cpu_est_clockrate(int cpu_id, uint64_t *rate) mtx_unlock_spin(&sched_lock); #endif - tsc_freq = (tsc2 - tsc1) * 1000; - *rate = tsc_freq; + /* + * Calculate the difference in readings, convert to Mhz, and + * subtract 0.5% of the total. Empirical testing has shown that + * overhead in DELAY() works out to approximately this value. + */ + tsc2 -= tsc1; + *rate = tsc2 * 1000 - tsc2 * 5; return (0); } |