static struct clocksource clocksource_tsc;
/*
- * We compare the TSC to the cycle_last value in the clocksource
+ * We used to 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
* due to the unsigned delta calculation of the time keeping core
* code, which is necessary to support wrapping clocksources like pm
* timer.
+ *
+ * This sanity check is now done in the core timekeeping code.
+ * checking the result of read_tsc() - cycle_last for being negative.
+ * That works because CLOCKSOURCE_MASK(64) does not mask out any bit.
*/
static cycle_t read_tsc(struct clocksource *cs)
{
- cycle_t ret = (cycle_t)get_cycles();
-
- return ret >= clocksource_tsc.cycle_last ?
- ret : clocksource_tsc.cycle_last;
-}
-
-static void resume_tsc(struct clocksource *cs)
-{
- if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3))
- clocksource_tsc.cycle_last = 0;
+ return (cycle_t)get_cycles();
}
+/*
+ * .mask MUST be CLOCKSOURCE_MASK(64). See comment above read_tsc()
+ */
static struct clocksource clocksource_tsc = {
.name = "tsc",
.rating = 300,
.read = read_tsc,
- .resume = resume_tsc,
.mask = CLOCKSOURCE_MASK(64),
.flags = CLOCK_SOURCE_IS_CONTINUOUS |
CLOCK_SOURCE_MUST_VERIFY,