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

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Message-ID: <CA+iXiiOR+dhXis5FMXnBw+rohgFe8gG3qk4=ChMTbG+Cdb1iwg@mail.gmail.com>
Date:	Thu, 11 Dec 2014 10:26:14 +0530
From:	Santosh Shukla <santosh.shukla@...aro.org>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
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 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.

And in case there is no timer in list; We shut down the
clk_evt_device. Therefore no spurious interrupt in either of two
possible cases.
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