static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
{
- unsigned long flags, prev_scale, *scale;
unsigned long long tsc_now, ns_now;
+ unsigned long flags, *scale;
local_irq_save(flags);
sched_clock_idle_sleep_event();
rdtscll(tsc_now);
ns_now = __cycles_2_ns(tsc_now);
- prev_scale = *scale;
if (cpu_khz)
*scale = (NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR)/cpu_khz;
* if the CPU frequency is scaled, TSC-based delays will need a different
* loops_per_jiffy value to function properly.
*/
-static unsigned int ref_freq = 0;
-static unsigned long loops_per_jiffy_ref = 0;
-static unsigned long cpu_khz_ref = 0;
+static unsigned int ref_freq;
+static unsigned long loops_per_jiffy_ref;
+static unsigned long cpu_khz_ref;
static int
time_cpufreq_notifier(struct notifier_block *nb, unsigned long val, void *data)
ref_freq, freq->new);
if (!(freq->flags & CPUFREQ_CONST_LOOPS)) {
tsc_khz = cpu_khz;
- preempt_disable();
- set_cyc2ns_scale(cpu_khz, smp_processor_id());
- preempt_enable();
+ set_cyc2ns_scale(cpu_khz, freq->cpu);
/*
* TSC based sched_clock turns
* to junk w/ cpufreq
/* clock source code */
-static unsigned long current_tsc_khz = 0;
+static unsigned long current_tsc_khz;
+static struct clocksource clocksource_tsc;
+/*
+ * We compare the TSC to the cycle_last value in the clocksource
+ * structure to avoid a nasty time-warp issue. This can be observed in
+ * a very small window right after one CPU updated cycle_last under
+ * xtime lock and the other CPU reads a TSC value which is smaller
+ * than the cycle_last reference value due to a TSC which is slighty
+ * behind. This delta is nowhere else observable, but in that case it
+ * results in a forward time jump in the range of hours due to the
+ * unsigned delta calculation of the time keeping core code, which is
+ * necessary to support wrapping clocksources like pm timer.
+ */
static cycle_t read_tsc(void)
{
cycle_t ret;
rdtscll(ret);
- return ret;
+ return ret >= clocksource_tsc.cycle_last ?
+ ret : clocksource_tsc.cycle_last;
}
static struct clocksource clocksource_tsc = {
int cpu;
if (!cpu_has_tsc)
- goto out_no_tsc;
+ return;
cpu_khz = calculate_cpu_khz();
tsc_khz = cpu_khz;
- if (!cpu_khz)
- goto out_no_tsc;
+ if (!cpu_khz) {
+ mark_tsc_unstable("could not calculate TSC khz");
+ return;
+ }
printk("Detected %lu.%03lu MHz processor.\n",
(unsigned long)cpu_khz / 1000,
tsc_enabled = 1;
clocksource_register(&clocksource_tsc);
-
- return;
-
-out_no_tsc:
- setup_clear_cpu_cap(X86_FEATURE_TSC);
}