> On Tue, 15 Aug 2017, Liang, Kan wrote: > > This patch which speed up the hrtimer > (https://lkml.org/lkml/2017/6/26/685) > > is decent to fix the spurious hard lockups. > > Tested-by: Kan Liang <kan.liang@xxxxxxxxx> > > > > Please consider to merge it into both mainline and stable tree. > > Well, it 'fixes' the problem, but at the same time it imposes a higher > frequency of hrtimer interrupts and a higher frequency of soft lockup > thread wakeups. I'm not convinced that this is the right thing to do, even > if the patch itself is simple and small. > > Did you run the patch which implements the low pass filter? Does it fix the > issue as well? It's slightly larger, but does not come with the downsides > of the real simple one. Appended for reference. I just finished the test for the low pass filter patch. Yes, it also fixes the watchdog false positive issue. Thanks, Kan > > Thanks, > > tglx > > 8<--------------------- > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -100,6 +100,7 @@ config X86 > select GENERIC_STRNCPY_FROM_USER > select GENERIC_STRNLEN_USER > select GENERIC_TIME_VSYSCALL > + select HARDLOCKUP_CHECK_TIMESTAMP if X86_64 > select HAVE_ACPI_APEI if ACPI > select HAVE_ACPI_APEI_NMI if ACPI > select HAVE_ALIGNED_STRUCT_PAGE if SLUB > --- a/include/linux/nmi.h > +++ b/include/linux/nmi.h > @@ -168,6 +168,14 @@ extern int sysctl_hardlockup_all_cpu_bac > #define sysctl_softlockup_all_cpu_backtrace 0 > #define sysctl_hardlockup_all_cpu_backtrace 0 > #endif > + > +#if defined(CONFIG_HARDLOCKUP_CHECK_TIMESTAMP) && \ > + defined(CONFIG_HARDLOCKUP_DETECTOR) > +void watchdog_update_hrtimer_threshold(u64 period); > +#else > +static inline void watchdog_update_hrtimer_threshold(u64 period) { } > +#endif > + > extern bool is_hardlockup(void); > struct ctl_table; > extern int proc_watchdog(struct ctl_table *, int , > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -240,6 +240,7 @@ static void set_sample_period(void) > * hardlockup detector generates a warning > */ > sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5); > + watchdog_update_hrtimer_threshold(sample_period); > } > > /* Commands for resetting the watchdog */ > --- a/kernel/watchdog_hld.c > +++ b/kernel/watchdog_hld.c > @@ -37,6 +37,62 @@ void arch_touch_nmi_watchdog(void) > } > EXPORT_SYMBOL(arch_touch_nmi_watchdog); > > +#ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP > +static DEFINE_PER_CPU(ktime_t, last_timestamp); > +static DEFINE_PER_CPU(unsigned int, nmi_rearmed); > +static ktime_t watchdog_hrtimer_sample_threshold __read_mostly; > + > +void watchdog_update_hrtimer_threshold(u64 period) > +{ > + /* > + * The hrtimer runs with a period of (watchdog_threshold * 2) / 5 > + * > + * So it runs effectively with 2.5 times the rate of the NMI > + * watchdog. That means the hrtimer should fire 2-3 times before > + * the NMI watchdog expires. The NMI watchdog on x86 is based on > + * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles > + * might run way faster than expected and the NMI fires in a > + * smaller period than the one deduced from the nominal CPU > + * frequency. Depending on the Turbo-Mode factor this might be fast > + * enough to get the NMI period smaller than the hrtimer watchdog > + * period and trigger false positives. > + * > + * The sample threshold is used to check in the NMI handler whether > + * the minimum time between two NMI samples has elapsed. That > + * prevents false positives. > + * > + * Set this to 4/5 of the actual watchdog threshold period so the > + * hrtimer is guaranteed to fire at least once within the real > + * watchdog threshold. > + */ > + watchdog_hrtimer_sample_threshold = period * 2; > +} > + > +static bool watchdog_check_timestamp(void) > +{ > + ktime_t delta, now = ktime_get_mono_fast_ns(); > + > + delta = now - __this_cpu_read(last_timestamp); > + if (delta < watchdog_hrtimer_sample_threshold) { > + /* > + * If ktime is jiffies based, a stalled timer would prevent > + * jiffies from being incremented and the filter would look > + * at a stale timestamp and never trigger. > + */ > + if (__this_cpu_inc_return(nmi_rearmed) < 10) > + return false; > + } > + __this_cpu_write(nmi_rearmed, 0); > + __this_cpu_write(last_timestamp, now); > + return true; > +} > +#else > +static inline bool watchdog_check_timestamp(void) > +{ > + return true; > +} > +#endif > + > static struct perf_event_attr wd_hw_attr = { > .type = PERF_TYPE_HARDWARE, > .config = PERF_COUNT_HW_CPU_CYCLES, > @@ -61,6 +117,9 @@ static void watchdog_overflow_callback(s > return; > } > > + if (!watchdog_check_timestamp()) > + return; > + > /* check for a hardlockup > * This is done by making sure our timer interrupt > * is incrementing. The timer interrupt should have > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -798,6 +798,13 @@ config HARDLOCKUP_DETECTOR_PERF > select SOFTLOCKUP_DETECTOR > > # > +# Enables a timestamp based low pass filter to compensate for perf based > +# hard lockup detection which runs too fast due to turbo modes. > +# > +config HARDLOCKUP_CHECK_TIMESTAMP > + bool > + > +# > # arch/ can define HAVE_HARDLOCKUP_DETECTOR_ARCH to provide their > own hard > # lockup detector rather than the perf based detector. > #