The only direct method to determine whether an HPET timer caused an interrupt is to read the Interrupt Status register. Unfortunately, reading HPET registers is slow and, therefore, it is not recommended to read them while in NMI context. Furthermore, status is not available if the interrupt is generated vi the Front Side Bus.
An indirect manner is to compute the expected value of the the time-stamp counter and, at the time of the interrupt and verify that its actual value is within a range of the expected value. Since the hardlockup detector operates in seconds, high precision is not needed. This implementation considers that the HPET caused the HMI if the time-stamp counter reads the expected value -/+ 1.5%. This value is selected is it is equivalent to 1/64 and the division can be performed using bit shifts. Experimentally, the error in the estimation is consistently less than 1%. Also, only read the time-stamp counter of the handling CPU (the one targeted by the HPET timer). This helps to avoid variability of the time stamp across CPUs. Cc: "H. Peter Anvin" <[email protected]> Cc: Ashok Raj <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Tony Luck <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Clemens Ladisch <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Philippe Ombredanne <[email protected]> Cc: Kate Stewart <[email protected]> Cc: "Rafael J. Wysocki" <[email protected]> Cc: Mimi Zohar <[email protected]> Cc: Jan Kiszka <[email protected]> Cc: Nick Desaulniers <[email protected]> Cc: Masahiro Yamada <[email protected]> Cc: Nayna Jain <[email protected]> Cc: "Ravi V. Shankar" <[email protected]> Cc: [email protected] Suggested-by: Andi Kleen <[email protected]> Signed-off-by: Ricardo Neri <[email protected]> --- arch/x86/include/asm/hpet.h | 2 ++ arch/x86/kernel/watchdog_hld_hpet.c | 28 +++++++++++++++++++++++++--- 2 files changed, 27 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/hpet.h b/arch/x86/include/asm/hpet.h index 15dc3b576496..09763340c911 100644 --- a/arch/x86/include/asm/hpet.h +++ b/arch/x86/include/asm/hpet.h @@ -123,6 +123,8 @@ struct hpet_hld_data { u32 num; u32 flags; u64 ticks_per_second; + u64 tsc_next; + u64 tsc_next_error; u32 handling_cpu; struct cpumask cpu_monitored_mask; struct msi_msg msi_msg; diff --git a/arch/x86/kernel/watchdog_hld_hpet.c b/arch/x86/kernel/watchdog_hld_hpet.c index cfa284da4bf6..65b4699f249a 100644 --- a/arch/x86/kernel/watchdog_hld_hpet.c +++ b/arch/x86/kernel/watchdog_hld_hpet.c @@ -55,6 +55,11 @@ static inline void set_comparator(struct hpet_hld_data *hdata, * * Reprogram the timer to expire within watchdog_thresh seconds in the future. * + * Also compute the expected value of the time-stamp counter at the time of + * expiration as well as a deviation from the expected value. The maximum + * deviation is of ~1.5%. This deviation can be easily computed by shifting + * by 6 positions the delta between the current and expected time-stamp values. + * * Returns: * * None @@ -62,7 +67,18 @@ static inline void set_comparator(struct hpet_hld_data *hdata, static void kick_timer(struct hpet_hld_data *hdata, bool force) { bool kick_needed = force || !(hdata->flags & HPET_DEV_PERI_CAP); - unsigned long new_compare, count; + unsigned long tsc_curr, tsc_delta, new_compare, count; + + /* Start obtaining the current TSC and HPET counts. */ + tsc_curr = rdtsc(); + + if (kick_needed) + count = get_count(); + + tsc_delta = (unsigned long)watchdog_thresh * (unsigned long)tsc_khz + * 1000L; + hdata->tsc_next = tsc_curr + tsc_delta; + hdata->tsc_next_error = tsc_delta >> 6; /* * Update the comparator in increments of watch_thresh seconds relative @@ -74,8 +90,6 @@ static void kick_timer(struct hpet_hld_data *hdata, bool force) */ if (kick_needed) { - count = get_count(); - new_compare = count + watchdog_thresh * hdata->ticks_per_second; set_comparator(hdata, new_compare); @@ -147,6 +161,14 @@ static void set_periodic(struct hpet_hld_data *hdata) */ static bool is_hpet_wdt_interrupt(struct hpet_hld_data *hdata) { + if (smp_processor_id() == hdata->handling_cpu) { + unsigned long tsc_curr; + + tsc_curr = rdtsc(); + if (abs(tsc_curr - hdata->tsc_next) < hdata->tsc_next_error) + return true; + } + return false; } -- 2.17.1
