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From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ricardo Neri <ricardo.neri@intel.com>,
	Stephane Eranian <eranian@google.com>,
	Kai-Heng Feng <kai.heng.feng@canonical.com>,
	Ingo Molnar <mingo@kernel.org>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Ashok Raj <ashok.raj@intel.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	x86@kernel.org, "Luis R. Rodriguez" <mcgrof@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Andi Kleen <andi.kleen@intel.com>,
	Waiman Long <longman@redhat.com>, Borislav Petkov <bp@suse.de>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Don Zickus <dzickus@redhat.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Frederic Weisbecker <frederic@kernel.org>,
	Nicholas Piggin <npiggin@gmail.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Byungchul Park <byungchul.park@lge.com>,
	Babu Moger <Babu.Moger@amd.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Tony Luck <tony.luck@intel.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	Jacob Pan <jacob.jun.pan@intel.com>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Colin Ian King <colin.king@canonical.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC PATCH v4 12/21] watchdog/hardlockup/hpet: Adjust timer expiration on the number of monitored CPUs
Date: Tue, 18 Jun 2019 15:46:54 -0700
Message-ID: <20190618224654.GB30488@ranerica-svr.sc.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1906112205170.2214@nanos.tec.linutronix.de>

On Tue, Jun 11, 2019 at 10:11:04PM +0200, Thomas Gleixner wrote:
> On Thu, 23 May 2019, Ricardo Neri wrote:
> > @@ -52,10 +59,10 @@ static void kick_timer(struct hpet_hld_data *hdata, bool force)
> >  		return;
> >  
> >  	if (hdata->has_periodic)
> > -		period = watchdog_thresh * hdata->ticks_per_second;
> > +		period = watchdog_thresh * hdata->ticks_per_cpu;
> >  
> >  	count = hpet_readl(HPET_COUNTER);
> > -	new_compare = count + watchdog_thresh * hdata->ticks_per_second;
> > +	new_compare = count + watchdog_thresh * hdata->ticks_per_cpu;
> >  	hpet_set_comparator(hdata->num, (u32)new_compare, (u32)period);
> 
> So with this you might get close to the point where you trip over the SMI
> induced madness where CPUs vanish for several milliseconds in some value
> add code. You really want to do a read back of the hpet to detect that. See
> the comment in the hpet code. RHEL 7/8 allow up to 768 logical CPUs....

Do you mean adding a readback to check if the new compare value is
greater than the current count? Similar to the check at the end of
hpet_next_event():

	return res < HPET_MIN_CYCLES ? -ETIME : 0;

In such a case, should it try to set the comparator again? I think it
should, as otherwise the hardlockup detector would stop working.

Thanks and BR,
Ricardo
> 
> Thanks,
> 
> 	tglx
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  reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-24  1:16 [RFC PATCH v4 00/21] Implement an HPET-based hardlockup detector Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 01/21] x86/msi: Add definition for NMI delivery mode Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 02/21] x86/hpet: Expose hpet_writel() in header Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 03/21] x86/hpet: Calculate ticks-per-second in a separate function Ricardo Neri
2019-06-14 15:54   ` Thomas Gleixner
2019-06-14 15:59     ` Thomas Gleixner
2019-06-18 22:48     ` Ricardo Neri
2019-06-18 23:13       ` Thomas Gleixner
2019-05-24  1:16 ` [RFC PATCH v4 04/21] x86/hpet: Add hpet_set_comparator() for periodic and one-shot modes Ricardo Neri
2019-06-14 18:17   ` Thomas Gleixner
2019-06-18 22:48     ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 05/21] x86/hpet: Reserve timer for the HPET hardlockup detector Ricardo Neri
2019-06-11 19:54   ` Thomas Gleixner
2019-06-14  1:14     ` Ricardo Neri
2019-06-14 16:10       ` Thomas Gleixner
2019-06-18 22:48         ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 06/21] x86/hpet: Configure the timer used by the " Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 07/21] watchdog/hardlockup: Define a generic function to detect hardlockups Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 08/21] watchdog/hardlockup: Decouple the hardlockup detector from perf Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 09/21] x86/nmi: Add a NMI_WATCHDOG NMI handler category Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 10/21] watchdog/hardlockup: Add function to enable NMI watchdog on all allowed CPUs at once Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 11/21] x86/watchdog/hardlockup: Add an HPET-based hardlockup detector Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 12/21] watchdog/hardlockup/hpet: Adjust timer expiration on the number of monitored CPUs Ricardo Neri
2019-06-11 20:11   ` Thomas Gleixner
2019-06-18 22:46     ` Ricardo Neri [this message]
2019-05-24  1:16 ` [RFC PATCH v4 13/21] x86/watchdog/hardlockup/hpet: Determine if HPET timer caused NMI Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 14/21] watchdog/hardlockup: Use parse_option_str() to handle "nmi_watchdog" Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 15/21] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 16/21] x86/watchdog: Add a shim hardlockup detector Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 17/21] x86/tsc: Switch to perf-based hardlockup detector if TSC become unstable Ricardo Neri
2019-06-07  0:35   ` Stephane Eranian via iommu
2019-06-07 14:14     ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 18/21] x86/apic: Add a parameter for the APIC delivery mode Ricardo Neri
2019-06-16  9:55   ` Thomas Gleixner
2019-06-18 22:47     ` Ricardo Neri
2019-06-18 23:15       ` Thomas Gleixner
2019-05-24  1:16 ` [RFC PATCH v4 19/21] iommu/vt-d: Rework prepare_irte() to support per-irq " Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 20/21] iommu/vt-d: hpet: Reserve an interrupt remampping table entry for watchdog Ricardo Neri
2019-06-16 18:42   ` Thomas Gleixner
2019-06-16 19:21   ` Thomas Gleixner
2019-06-17  8:25     ` Thomas Gleixner
2019-06-17 21:38       ` Stephane Eranian via iommu
2019-06-17 23:08         ` Thomas Gleixner
2019-06-19 15:43           ` Jacob Pan
2019-06-21 15:33             ` Thomas Gleixner
2019-06-21 17:31               ` Jacob Pan
2019-06-21 18:39                 ` Jacob Pan
2019-06-21 20:05                   ` Thomas Gleixner
2019-06-21 23:55                     ` Ricardo Neri
2019-06-22  7:21                       ` Thomas Gleixner
2019-06-18 22:45       ` Ricardo Neri
2019-05-24  1:16 ` [RFC PATCH v4 21/21] x86/watchdog/hardlockup/hpet: Support interrupt remapping Ricardo Neri
2019-06-16  8:44   ` Thomas Gleixner
2019-06-16  8:53     ` Thomas Gleixner

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