diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/time/Kconfig | 6 | ||||
| -rw-r--r-- | kernel/time/clocksource.c | 72 |
2 files changed, 56 insertions, 22 deletions
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index a41753be1a2b..bae8f11070be 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -200,10 +200,14 @@ config CLOCKSOURCE_WATCHDOG_MAX_SKEW_US int "Clocksource watchdog maximum allowable skew (in μs)" depends on CLOCKSOURCE_WATCHDOG range 50 1000 - default 100 + default 125 help Specify the maximum amount of allowable watchdog skew in microseconds before reporting the clocksource to be unstable. + The default is based on a half-second clocksource watchdog + interval and NTP's maximum frequency drift of 500 parts + per million. If the clocksource is good enough for NTP, + it is good enough for the clocksource watchdog! endmenu endif diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 9cf32ccda715..91836b727cef 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -96,6 +96,11 @@ static int finished_booting; static u64 suspend_start; /* + * Interval: 0.5sec. + */ +#define WATCHDOG_INTERVAL (HZ >> 1) + +/* * Threshold: 0.0312s, when doubled: 0.0625s. * Also a default for cs->uncertainty_margin when registering clocks. */ @@ -106,11 +111,14 @@ static u64 suspend_start; * clocksource surrounding a read of the clocksource being validated. * This delay could be due to SMIs, NMIs, or to VCPU preemptions. Used as * a lower bound for cs->uncertainty_margin values when registering clocks. + * + * The default of 500 parts per million is based on NTP's limits. + * If a clocksource is good enough for NTP, it is good enough for us! */ #ifdef CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US #define MAX_SKEW_USEC CONFIG_CLOCKSOURCE_WATCHDOG_MAX_SKEW_US #else -#define MAX_SKEW_USEC 100 +#define MAX_SKEW_USEC (125 * WATCHDOG_INTERVAL / HZ) #endif #define WATCHDOG_MAX_SKEW (MAX_SKEW_USEC * NSEC_PER_USEC) @@ -140,11 +148,6 @@ static inline void clocksource_watchdog_unlock(unsigned long *flags) static int clocksource_watchdog_kthread(void *data); static void __clocksource_change_rating(struct clocksource *cs, int rating); -/* - * Interval: 0.5sec. - */ -#define WATCHDOG_INTERVAL (HZ >> 1) - static void clocksource_watchdog_work(struct work_struct *work) { /* @@ -257,8 +260,8 @@ static enum wd_read_status cs_watchdog_read(struct clocksource *cs, u64 *csnow, goto skip_test; } - pr_warn("timekeeping watchdog on CPU%d: %s read-back delay of %lldns, attempt %d, marking unstable\n", - smp_processor_id(), watchdog->name, wd_delay, nretries); + pr_warn("timekeeping watchdog on CPU%d: wd-%s-wd excessive read-back delay of %lldns vs. limit of %ldns, wd-wd read-back delay only %lldns, attempt %d, marking %s unstable\n", + smp_processor_id(), cs->name, wd_delay, WATCHDOG_MAX_SKEW, wd_seq_delay, nretries, cs->name); return WD_READ_UNSTABLE; skip_test: @@ -384,6 +387,15 @@ void clocksource_verify_percpu(struct clocksource *cs) } EXPORT_SYMBOL_GPL(clocksource_verify_percpu); +static inline void clocksource_reset_watchdog(void) +{ + struct clocksource *cs; + + list_for_each_entry(cs, &watchdog_list, wd_list) + cs->flags &= ~CLOCK_SOURCE_WATCHDOG; +} + + static void clocksource_watchdog(struct timer_list *unused) { u64 csnow, wdnow, cslast, wdlast, delta; @@ -391,6 +403,7 @@ static void clocksource_watchdog(struct timer_list *unused) int64_t wd_nsec, cs_nsec; struct clocksource *cs; enum wd_read_status read_ret; + unsigned long extra_wait = 0; u32 md; spin_lock(&watchdog_lock); @@ -410,13 +423,30 @@ static void clocksource_watchdog(struct timer_list *unused) read_ret = cs_watchdog_read(cs, &csnow, &wdnow); - if (read_ret != WD_READ_SUCCESS) { - if (read_ret == WD_READ_UNSTABLE) - /* Clock readout unreliable, so give it up. */ - __clocksource_unstable(cs); + if (read_ret == WD_READ_UNSTABLE) { + /* Clock readout unreliable, so give it up. */ + __clocksource_unstable(cs); continue; } + /* + * When WD_READ_SKIP is returned, it means the system is likely + * under very heavy load, where the latency of reading + * watchdog/clocksource is very big, and affect the accuracy of + * watchdog check. So give system some space and suspend the + * watchdog check for 5 minutes. + */ + if (read_ret == WD_READ_SKIP) { + /* + * As the watchdog timer will be suspended, and + * cs->last could keep unchanged for 5 minutes, reset + * the counters. + */ + clocksource_reset_watchdog(); + extra_wait = HZ * 300; + break; + } + /* Clocksource initialized ? */ if (!(cs->flags & CLOCK_SOURCE_WATCHDOG) || atomic_read(&watchdog_reset_pending)) { @@ -443,12 +473,20 @@ static void clocksource_watchdog(struct timer_list *unused) /* Check the deviation from the watchdog clocksource. */ md = cs->uncertainty_margin + watchdog->uncertainty_margin; if (abs(cs_nsec - wd_nsec) > md) { + u64 cs_wd_msec; + u64 wd_msec; + u32 wd_rem; + pr_warn("timekeeping watchdog on CPU%d: Marking clocksource '%s' as unstable because the skew is too large:\n", smp_processor_id(), cs->name); pr_warn(" '%s' wd_nsec: %lld wd_now: %llx wd_last: %llx mask: %llx\n", watchdog->name, wd_nsec, wdnow, wdlast, watchdog->mask); pr_warn(" '%s' cs_nsec: %lld cs_now: %llx cs_last: %llx mask: %llx\n", cs->name, cs_nsec, csnow, cslast, cs->mask); + cs_wd_msec = div_u64_rem(cs_nsec - wd_nsec, 1000U * 1000U, &wd_rem); + wd_msec = div_u64_rem(wd_nsec, 1000U * 1000U, &wd_rem); + pr_warn(" Clocksource '%s' skewed %lld ns (%lld ms) over watchdog '%s' interval of %lld ns (%lld ms)\n", + cs->name, cs_nsec - wd_nsec, cs_wd_msec, watchdog->name, wd_nsec, wd_msec); if (curr_clocksource == cs) pr_warn(" '%s' is current clocksource.\n", cs->name); else if (curr_clocksource) @@ -512,7 +550,7 @@ static void clocksource_watchdog(struct timer_list *unused) * pair clocksource_stop_watchdog() clocksource_start_watchdog(). */ if (!timer_pending(&watchdog_timer)) { - watchdog_timer.expires += WATCHDOG_INTERVAL; + watchdog_timer.expires += WATCHDOG_INTERVAL + extra_wait; add_timer_on(&watchdog_timer, next_cpu); } out: @@ -537,14 +575,6 @@ static inline void clocksource_stop_watchdog(void) watchdog_running = 0; } -static inline void clocksource_reset_watchdog(void) -{ - struct clocksource *cs; - - list_for_each_entry(cs, &watchdog_list, wd_list) - cs->flags &= ~CLOCK_SOURCE_WATCHDOG; -} - static void clocksource_resume_watchdog(void) { atomic_inc(&watchdog_reset_pending); |