diff options
Diffstat (limited to 'arch/x86/kernel/tsc_32.c')
| -rw-r--r-- | arch/x86/kernel/tsc_32.c | 23 |
1 files changed, 18 insertions, 5 deletions
diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c index 3d7e6e9fa6c..e4790728b22 100644 --- a/arch/x86/kernel/tsc_32.c +++ b/arch/x86/kernel/tsc_32.c @@ -221,9 +221,9 @@ EXPORT_SYMBOL(recalibrate_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) @@ -283,15 +283,28 @@ core_initcall(cpufreq_tsc); /* 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 = { |