/*
* TSC-warp measurement loop running on both CPUs. This is not called
* if there is no TSC.
*/
static cycles_t check_tsc_warp(unsigned int timeout)
{
cycles_t start, now, prev, end, cur_max_warp = 0;
int i, cur_warps = 0;
start = rdtsc_ordered();
/*
* The measurement runs for 'timeout' msecs:
*/
end = start + (cycles_t) tsc_khz * timeout;
now = start;
for (i = 0; ; i++) {
/*
* We take the global lock, measure TSC, save the
* previous TSC that was measured (possibly on
* another CPU) and update the previous TSC timestamp.
*/
arch_spin_lock(&sync_lock);
prev = last_tsc;
now = rdtsc_ordered();
last_tsc = now;
arch_spin_unlock(&sync_lock);
/*
* Be nice every now and then (and also check whether
* measurement is done [we also insert a 10 million
* loops safety exit, so we dont lock up in case the
* TSC readout is totally broken]):
*/
if (unlikely(!(i & 7))) {
if (now > end || i > 10000000)
break;
cpu_relax();
touch_nmi_watchdog();
}
/*
* Outside the critical section we can now see whether
* we saw a time-warp of the TSC going backwards:
*/
if (unlikely(prev > now)) {
arch_spin_lock(&sync_lock);
max_warp = max(max_warp, prev - now);
cur_max_warp = max_warp;
/*
* Check whether this bounces back and forth. Only
* one CPU should observe time going backwards.
*/
if (cur_warps != nr_warps)
random_warps++;
nr_warps++;
cur_warps = nr_warps;
arch_spin_unlock(&sync_lock);
}
}
WARN(!(now-start),
"Warning: zero tsc calibration delta: %Ld [max: %Ld]\n",
now-start, end-start);
return cur_max_warp;
}
static inline u64 msr_read_counter(struct perf_event *event)
{
u64 now;
if (event->hw.event_base)
rdmsrl(event->hw.event_base, now);
else
now = rdtsc_ordered();
return now;
}
/*
* trace_clock_x86_tsc(): A clock that is just the cycle counter.
*
* Unlike the other clocks, this is not in nanoseconds.
*/
u64 notrace trace_clock_x86_tsc(void)
{
return rdtsc_ordered();
}
