Messages in this thread | | | Date | Tue, 9 Apr 2019 13:28:17 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH v2 12/14] x86/watchdog/hardlockup/hpet: Determine if HPET timer caused NMI |
| |
On Wed, Feb 27, 2019 at 08:05:16AM -0800, Ricardo Neri wrote: > @@ -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;
What do we need a per hld_data tsc_next_error for? It is basically a global 'constant'.
> /* > * 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 is u64
> + > + tsc_curr = rdtsc(); > + if (abs(tsc_curr - hdata->tsc_next) < hdata->tsc_next_error) > + return true;
You can write that as:
(tsc_curr - hdata->tsc_next) + tsc_error < 2*tsc_error
which doesn't contain any branches what so ever.
> + } > + > return false; > }
| |