linux-kernel - Re: [Query] Spurious interrupts from clockevent device on X86 Ivybridge

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Date:	Fri, 12 Dec 2014 17:17:03 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Santosh Shukla <santosh.shukla@...aro.org>
CC:	Viresh Kumar <viresh.kumar@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kevin Hilman <khilman@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [Query] Spurious interrupts from clockevent device on X86 Ivybridge

On 12/11/2014 10:26 AM, Santosh Shukla wrote:
> On 11 December 2014 at 10:14, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote:
>> On 12/10/2014 06:22 PM, Viresh Kumar wrote:
>>> On 10 December 2014 at 18:03, Preeti U Murthy <preeti@...ux.vnet.ibm.com> wrote:
>>>
>>>> Right. We get an interrupt when nobody had asked for it to be delivered
>>>> or had asked for it to be delivered and later canceled the request. It
>>>> is most often in the latter situation, that there can be race
>>>> conditions. If these race conditions are not taken care of, they can
>>>> result in spurious interrupts.
>>>
>>> But the delta time will be very small then, right ?
>>
>> I was talking of the case where we get an interrupt from the clockevent
>> device but dont find the hrtimer to service and not really of an anomaly
>> in timekeeping.
>>    For instance one of the issues that we had seen earlier wherein we
>> cancel the tick-sched-timer before going tickless, but since we had
>> programmed the clock event device to fire, we get a spurious interrupt.
>>
> 
> I verified this case before reporting; In my case tick_sched_timer do
> get cancelled before expire duration but then  clk_evt_device get
> reprogrammed for next time node in list.  __remove_hrtimer() takes
> care of that.

Right. The scenario I described happens in the Low Resolution Mode. You
are right, this does not happen in the High Resolution Mode.

Regards
Preeti U Murthy

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