diff options
| -rw-r--r-- | arch/x86/kernel/tsc_32.c | 15 | ||||
| -rw-r--r-- | arch/x86/kernel/tsc_64.c | 23 | ||||
| -rw-r--r-- | kernel/time/timekeeping.c | 2 |
3 files changed, 36 insertions, 4 deletions
diff --git a/arch/x86/kernel/tsc_32.c b/arch/x86/kernel/tsc_32.c index 06af8cf8251f..e4790728b224 100644 --- a/arch/x86/kernel/tsc_32.c +++ b/arch/x86/kernel/tsc_32.c @@ -284,14 +284,27 @@ core_initcall(cpufreq_tsc); /* clock source code */ 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 = { diff --git a/arch/x86/kernel/tsc_64.c b/arch/x86/kernel/tsc_64.c index ceeba01e7f47..fcc16e58609e 100644 --- a/arch/x86/kernel/tsc_64.c +++ b/arch/x86/kernel/tsc_64.c @@ -11,6 +11,7 @@ #include <asm/hpet.h> #include <asm/timex.h> #include <asm/timer.h> +#include <asm/vgtod.h> static int notsc __initdata = 0; @@ -287,18 +288,34 @@ int __init notsc_setup(char *s) __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 = { diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index a3fa587c350c..2d6087c7cf98 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -178,6 +178,7 @@ static void change_clocksource(void) if (clock == new) return; + new->cycle_last = 0; now = clocksource_read(new); nsec = __get_nsec_offset(); timespec_add_ns(&xtime, nsec); @@ -295,6 +296,7 @@ static int timekeeping_resume(struct sys_device *dev) timespec_add_ns(&xtime, timekeeping_suspend_nsecs); update_xtime_cache(0); /* re-base the last cycle value */ + clock->cycle_last = 0; clock->cycle_last = clocksource_read(clock); clock->error = 0; timekeeping_suspended = 0; |