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From: Thomas Gleixner <tglx@linutronix.de>
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Andi Kleen <andi.kleen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>, Borislav Petkov <bp@suse.de>,
	Tony Luck <tony.luck@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	x86@kernel.org, sparclinux@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	Jacob Pan <jacob.jun.pan@intel.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Don Zickus <dzickus@redhat.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Frederic Weisbecker <frederic@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Babu Moger <babu.moger@oracle.com>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Colin Ian King <colin.king@canonical.com>,
	Byungchul Park <byungchul.park@lge.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	Waiman Long <longman@redhat.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Christoffer Dall <cdall@linaro.org>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Kai-Heng Feng <kai.heng.feng@canonical.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	David Rientjes <rientjes@google.com>,
	iommu@lists.linux-foundation.org
Subject: Re: [RFC PATCH 17/23] watchdog/hardlockup/hpet: Convert the timer's interrupt to NMI
Date: Wed, 20 Jun 2018 09:47:53 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.21.1806200940210.10546@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180620001535.GA27531@voyager>

On Tue, 19 Jun 2018, Ricardo Neri wrote:
> On Sat, Jun 16, 2018 at 03:24:49PM +0200, Thomas Gleixner wrote:
> > The status register is useless in case of MSI. MSI is edge triggered ....
> > 
> > The only register which gives you proper information is the counter
> > register itself. That adds an massive overhead to each NMI, because the
> > counter register access is synchronized to the HPET clock with hardware
> > magic. Plus on larger systems, the HPET access is cross node and even
> > slower.
> 
> It starts to sound that the HPET is too slow to drive the hardlockup detector.
> 
> Would it be possible to envision a variant of this implementation? In this
> variant, the HPET only targets a single CPU. The actual hardlockup detector
> is implemented by this single CPU sending interprocessor interrupts to the
> rest of the CPUs.

And these IPIs must be NMIs which need to have a software based indicator
that the watchdog needs to be checked, which is going to create yet another
can of race conditions and in the worst case 'unknown NMI' splats. Not
pretty either.

Thanks,

	tglx

  parent reply	other threads:[~2018-06-20  8:30 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-13  0:57 [RFC PATCH 00/23] Implement an HPET-based hardlockup detector Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 01/23] x86/apic: Add a parameter for the APIC delivery mode Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 02/23] genirq: Introduce IRQD_DELIVER_AS_NMI Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 03/23] genirq: Introduce IRQF_DELIVER_AS_NMI Ricardo Neri
2018-06-13  8:34   ` Peter Zijlstra
2018-06-13  8:59     ` Julien Thierry
2018-06-13  9:20       ` Thomas Gleixner
2018-06-13  9:36         ` Julien Thierry
2018-06-13  9:49           ` Julien Thierry
2018-06-13  9:57           ` Thomas Gleixner
2018-06-13 10:25             ` Julien Thierry
2018-06-13 10:06         ` Marc Zyngier
2018-06-15  2:12           ` Ricardo Neri
2018-06-15  8:01             ` Julien Thierry
2018-06-16  0:39               ` Ricardo Neri
2018-06-16 13:36                 ` Thomas Gleixner
2018-06-13  0:57 ` [RFC PATCH 04/23] iommu/vt-d/irq_remapping: Add support for IRQCHIP_CAN_DELIVER_AS_NMI Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 05/23] x86/msi: " Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 06/23] x86/ioapic: Add support for IRQCHIP_CAN_DELIVER_AS_NMI with interrupt remapping Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 07/23] x86/hpet: Expose more functions to read and write registers Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 08/23] x86/hpet: Calculate ticks-per-second in a separate function Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 09/23] x86/hpet: Reserve timer for the HPET hardlockup detector Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 10/23] x86/hpet: Relocate flag definitions to a header file Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 11/23] x86/hpet: Configure the timer used by the hardlockup detector Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 12/23] kernel/watchdog: Introduce a struct for NMI watchdog operations Ricardo Neri
2018-06-13  7:41   ` Nicholas Piggin
2018-06-13  8:42     ` Peter Zijlstra
2018-06-13  9:26       ` Thomas Gleixner
2018-06-13 11:52         ` Nicholas Piggin
2018-06-14  1:31           ` Ricardo Neri
2018-06-14  2:32             ` Nicholas Piggin
2018-06-14  8:32               ` Thomas Gleixner
2018-06-15  2:21               ` Ricardo Neri
2018-06-14  1:26       ` Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 13/23] watchdog/hardlockup: Define a generic function to detect hardlockups Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 14/23] watchdog/hardlockup: Decouple the hardlockup detector from perf Ricardo Neri
2018-06-13  8:43   ` Peter Zijlstra
2018-06-14  1:19     ` Ricardo Neri
2018-06-14  1:41       ` Nicholas Piggin
2018-06-15  2:23         ` Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 15/23] kernel/watchdog: Add a function to obtain the watchdog_allowed_mask Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 16/23] watchdog/hardlockup: Add an HPET-based hardlockup detector Ricardo Neri
2018-06-13  5:23   ` Randy Dunlap
2018-06-14  1:00     ` Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 17/23] watchdog/hardlockup/hpet: Convert the timer's interrupt to NMI Ricardo Neri
2018-06-13  9:07   ` Peter Zijlstra
2018-06-15  2:07     ` Ricardo Neri
2018-06-13  9:40   ` Thomas Gleixner
2018-06-15  2:03     ` Ricardo Neri
2018-06-15  9:19       ` Thomas Gleixner
2018-06-16  0:51         ` Ricardo Neri
2018-06-16 13:24           ` Thomas Gleixner
2018-06-20  0:15             ` Ricardo Neri
2018-06-20  0:25               ` Randy Dunlap
2018-06-21  0:25                 ` Ricardo Neri
2018-06-20  7:47               ` Thomas Gleixner [this message]
2018-06-13  0:57 ` [RFC PATCH 18/23] watchdog/hardlockup/hpet: Add the NMI watchdog operations Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 19/23] watchdog/hardlockup: Make arch_touch_nmi_watchdog() to hpet-based implementation Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 20/23] watchdog/hardlockup/hpet: Rotate interrupt among all monitored CPUs Ricardo Neri
2018-06-13  9:48   ` Thomas Gleixner
2018-06-15  2:16     ` Ricardo Neri
2018-06-15 10:29       ` Thomas Gleixner
2018-06-16  0:46         ` Ricardo Neri
2018-06-16 13:27           ` Thomas Gleixner
2018-06-13  0:57 ` [RFC PATCH 21/23] watchdog/hardlockup/hpet: Adjust timer expiration on the number of " Ricardo Neri
2018-06-13  0:57 ` [RFC PATCH 22/23] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter Ricardo Neri
2018-06-13  5:26   ` Randy Dunlap
2018-06-14  0:58     ` Ricardo Neri
2018-06-14  3:30       ` Randy Dunlap
2018-06-13  0:57 ` [RFC PATCH 23/23] watchdog/hardlockup: Activate the HPET-based lockup detector Ricardo Neri

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