linux-kernel - Re: Random abnormal high CPU sys usage related to timer

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Message-ID: <alpine.DEB.2.20.1608291244470.5714@nanos>
Date:   Mon, 29 Aug 2016 12:45:18 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mac Lin <mkl0301@...il.com>
cc:     Vegard Nossum <vegard.nossum@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Random abnormal high CPU sys usage related to timer

On Sat, 27 Aug 2016, Mac Lin wrote:
> Hi Vegard,
> Thanks for the prompt response.
> The commit is introduced since 4.6, but the issue can be reproduced at
> 3.10 (earliest I have ever test). And testing on buildroot+4.7 with
> the commit reverted, the issue still happen.
> 
> In fact, I did a test that ran a script that keep increase a counter
> for 10 seconds on the same CPU. If I ran 2 of it, the number is half
> of running 1. But if I ran it while the issue happened, the counter
> reported is around the same value as the 1 process case. So I doubt
> that it might be an issue of reported number.
> 
> Is there other way to ensure the CPU is "really" doing something?

Tracing will tell you exactly what's going on in the system.

Thanks,

	tglx