notes/pvclock_clocksource_read at master · denis-plotnikov/notes · GitHub

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u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src, u64 *tsc_stamp)
{
        unsigned version;
        u64 ret;
        u64 last;
        u8 flags;
        u64 tsc;
        static bool stable_cached = false;

        do {
                version = pvclock_read_begin(src);
                tsc = rdtsc_ordered();
                if (tsc_stamp)
                        *tsc_stamp = tsc;
                ret = __pvclock_read_cycles(src, tsc);
                flags = src->flags;
        } while (pvclock_read_retry(src, version));

        if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
                src->flags &= ~PVCLOCK_GUEST_STOPPED;
                pvclock_touch_watchdogs();
        }

        if (likely(valid_flags & PVCLOCK_TSC_STABLE_BIT)) {
                // u64 cs_stable_now = !!(flags & PVCLOCK_TSC_STABLE_BIT);
                // u64 st = cs_stable_now;
                // if (unlikely(cs_stable_now != atomic64_xchg(&cs_stable, cs_stable_now))) {
                //      printk("Clocksource changed: now: %llu flags: %u now copy: %llu", cs_stable_now, flags, st);
                //      clocksource_changes_notify();
                //}
                //
                bool stable_now = !!(flags & PVCLOCK_TSC_STABLE_BIT);
                if (stable_cached != stable_now) {
                        printk("Clocksource changed: now: %u was: %u flags: %u", stable_now, stable_cached, flags);
                        stable_cached = stable_now;
                        clocksource_changes_notify();
                }
                if (stable_now)
                        return ret;
        }


/* this works as good as hell
        if (likely(valid_flags & PVCLOCK_TSC_STABLE_BIT)) {
                bool stable_now = !!(flags & PVCLOCK_TSC_STABLE_BIT);
                long stable_last = atomic64_read(&cs_stable);
                if (stable_now != stable_last) {
                        printk("Clocksource changed: now: %u was: %ld flags: %u", stable_now, stable_last, flags);
                        if (stable_last == atomic64_cmpxchg(&cs_stable, stable_last, stable_now)) {
                                printk("Send notifier");
                                clocksource_changes_notify();
                        }
                }
                if (stable_now)
                        return ret;
        }
*/