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Date: Fri, 12 Dec 2014 17:17:03 +0530
From: Preeti U Murthy <preeti@linux.vnet.ibm.com>
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To: Santosh Shukla <santosh.shukla@linaro.org>
CC: Viresh Kumar <viresh.kumar@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [Query] Spurious interrupts from clockevent device on X86 Ivybridge
References: <CA+iXiiOhPxvJKR5-9U_9Hd6mOnXJadBS+WRZhtv3yPw2r8KgJQ@mail.gmail.com> <54883DB6.10504@linux.vnet.ibm.com> <CAKohpokJxXe2RNc4Jqb20PJo2adr49nKBbzdXzYk9=H4kNjfRQ@mail.gmail.com> <54892111.3000102@linux.vnet.ibm.com> <CA+iXiiOR+dhXis5FMXnBw+rohgFe8gG3qk4=ChMTbG+Cdb1iwg@mail.gmail.com>
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On 12/11/2014 10:26 AM, Santosh Shukla wrote:
> On 11 December 2014 at 10:14, Preeti U Murthy <preeti@linux.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@linux.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