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Date: Tue, 9 Apr 2019 18:19:57 -0700 From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>, Ashok Raj <ashok.raj@...el.com>, Andi Kleen <andi.kleen@...el.com>, "Ravi V. Shankar" <ravi.v.shankar@...el.com>, x86@...nel.org, linux-kernel@...r.kernel.org, Ricardo Neri <ricardo.neri@...el.com>, "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>, Clemens Ladisch <clemens@...isch.de>, Arnd Bergmann <arnd@...db.de>, Philippe Ombredanne <pombredanne@...b.com>, Kate Stewart <kstewart@...uxfoundation.org>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Mimi Zohar <zohar@...ux.ibm.com>, Jan Kiszka <jan.kiszka@...mens.com>, Nick Desaulniers <ndesaulniers@...gle.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Nayna Jain <nayna@...ux.ibm.com> Subject: Re: [RFC PATCH v2 12/14] x86/watchdog/hardlockup/hpet: Determine if HPET timer caused NMI On Tue, Apr 09, 2019 at 01:28:17PM +0200, Peter Zijlstra wrote: > 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'. > This is true. I thought I'd keep all the needed variables in a single struct to make the code more readable. I guess, I did not achieve that goal. I'll put it as a static global variable. > > /* > > * 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 In x86_64, isn't u64 an unsigned long? Do you mean to consider the 32-bit case? > > > + > > + 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. > Sure, I'll add this change. Thanks and BR, Ricardo
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