#include <asm/hpet.h>
#include <asm/timex.h>
#include <asm/timer.h>
+#include <asm/vgtod.h>
static int notsc __initdata = 0;
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;
/* hpet or pmtimer available ? */
if (!hpet && !pm1 && !pm2) {
printk(KERN_INFO "TSC calibrated against PIT\n");
- return;
+ goto out;
}
/* Check, whether the sampling was disturbed by an SMI */
if (tsc1 == ULONG_MAX || tsc2 == ULONG_MAX) {
printk(KERN_WARNING "TSC calibration disturbed by SMI, "
"using PIT calibration result\n");
- return;
+ goto out;
}
tsc2 = (tsc2 - tsc1) * 1000000L;
tsc_khz = tsc2 / tsc1;
+out:
for_each_possible_cpu(cpu)
set_cyc2ns_scale(tsc_khz, cpu);
}
__setup("notsc", notsc_setup);
+static struct clocksource clocksource_tsc;
-/* clock source code: */
+/*
+ * We compare the TSC to the cycle_last value in the clocksource
+ * structure to avoid a nasty time-warp. This can be observed in a
+ * very small window right after one CPU updated cycle_last under
+ * xtime/vsyscall_gtod 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 = (cycle_t)get_cycles();
- return ret;
+
+ return ret >= clocksource_tsc.cycle_last ?
+ ret : clocksource_tsc.cycle_last;
}
static cycle_t __vsyscall_fn vread_tsc(void)
{
cycle_t ret = (cycle_t)vget_cycles();
- return ret;
+
+ return ret >= __vsyscall_gtod_data.clock.cycle_last ?
+ ret : __vsyscall_gtod_data.clock.cycle_last;
}
static struct clocksource clocksource_tsc = {