diff options
| -rw-r--r-- | sys/x86/x86/tsc.c | 44 |
1 files changed, 38 insertions, 6 deletions
diff --git a/sys/x86/x86/tsc.c b/sys/x86/x86/tsc.c index 3c0445f..bd38703 100644 --- a/sys/x86/x86/tsc.c +++ b/sys/x86/x86/tsc.c @@ -79,7 +79,8 @@ static void tsc_freq_changed(void *arg, const struct cf_level *level, int status); static void tsc_freq_changing(void *arg, const struct cf_level *level, int *status); -static unsigned tsc_get_timecount(struct timecounter *tc); +static unsigned tsc_get_timecount(struct timecounter *tc); +static unsigned tsc_get_timecount_lowres(struct timecounter *tc); static void tsc_levels_changed(void *arg, int unit); static struct timecounter tsc_timecounter = { @@ -392,11 +393,19 @@ test_smp_tsc(void) static void init_TSC_tc(void) { + uint64_t max_freq; + int shift; if ((cpu_feature & CPUID_TSC) == 0 || tsc_disabled) return; /* + * Limit timecounter frequency to fit in an int and prevent it from + * overflowing too fast. + */ + max_freq = UINT_MAX; + + /* * We can not use the TSC if we support APM. Precise timekeeping * on an APM'ed machine is at best a fools pursuit, since * any and all of the time spent in various SMM code can't @@ -418,13 +427,27 @@ init_TSC_tc(void) * We can not use the TSC in SMP mode unless the TSCs on all CPUs are * synchronized. If the user is sure that the system has synchronized * TSCs, set kern.timecounter.smp_tsc tunable to a non-zero value. + * We also limit the frequency even lower to avoid "temporal anomalies" + * as much as possible. */ - if (smp_cpus > 1) + if (smp_cpus > 1) { tsc_timecounter.tc_quality = test_smp_tsc(); + max_freq >>= 8; + } #endif init: + for (shift = 0; shift < 32 && (tsc_freq >> shift) > max_freq; shift++) + ; + if (shift > 0) { + tsc_timecounter.tc_get_timecount = tsc_get_timecount_lowres; + tsc_timecounter.tc_name = "TSC-low"; + if (bootverbose) + printf("TSC timecounter discards lower %d bit(s).\n", + shift); + } if (tsc_freq != 0) { - tsc_timecounter.tc_frequency = tsc_freq; + tsc_timecounter.tc_frequency = tsc_freq >> shift; + tsc_timecounter.tc_priv = (void *)(intptr_t)shift; tc_init(&tsc_timecounter); } } @@ -496,7 +519,8 @@ tsc_freq_changed(void *arg, const struct cf_level *level, int status) /* Total setting for this level gives the new frequency in MHz. */ freq = (uint64_t)level->total_set.freq * 1000000; atomic_store_rel_64(&tsc_freq, freq); - atomic_store_rel_64(&tsc_timecounter.tc_frequency, freq); + tsc_timecounter.tc_frequency = + freq >> (int)(intptr_t)tsc_timecounter.tc_priv; } static int @@ -511,7 +535,8 @@ sysctl_machdep_tsc_freq(SYSCTL_HANDLER_ARGS) error = sysctl_handle_64(oidp, &freq, 0, req); if (error == 0 && req->newptr != NULL) { atomic_store_rel_64(&tsc_freq, freq); - atomic_store_rel_64(&tsc_timecounter.tc_frequency, freq); + tsc_timecounter.tc_frequency = + freq >> (int)(intptr_t)tsc_timecounter.tc_priv; } return (error); } @@ -520,8 +545,15 @@ SYSCTL_PROC(_machdep, OID_AUTO, tsc_freq, CTLTYPE_U64 | CTLFLAG_RW, 0, 0, sysctl_machdep_tsc_freq, "QU", "Time Stamp Counter frequency"); static u_int -tsc_get_timecount(struct timecounter *tc) +tsc_get_timecount(struct timecounter *tc __unused) { return (rdtsc32()); } + +static u_int +tsc_get_timecount_lowres(struct timecounter *tc) +{ + + return (rdtsc() >> (int)(intptr_t)tc->tc_priv); +} |
