linux-kernel - Re: [PATCH] nohz: Fix collision between tick and other hrtimers

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Message-ID: <20161226164015.GA2375@lerouge>
Date:   Mon, 26 Dec 2016 17:40:19 +0100
From:   Frederic Weisbecker <fweisbec@...il.com>
To:     Rik van Riel <riel@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        James Hartsock <hartsjc@...hat.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] nohz: Fix collision between tick and other hrtimers

On Sun, Dec 25, 2016 at 09:56:57PM -0500, Rik van Riel wrote:
> On Sat, 2016-12-24 at 17:15 +0100, Frederic Weisbecker wrote:
> > When the tick is stopped and an interrupt occurs afterward, we check
> > on
> > that interrupt exit if the next tick needs to be rescheduled. If it
> > doesn't need any update, we don't want to do anything.
> > 
> > In order to check if the tick needs an update, we compare it against
> > the
> > clockevent device deadline. Now that's a problem because the
> > clockevent
> > device is at a lower level than the tick itself if it is implemented
> > on top of hrtimer.
> 
> Ohhhhh, good find. That is one subtle bug.

Oh yeah, it took me several month to debug that one :-) !

> 
> Acked-by: Rik van Riel <riel@...hat.com>

Thanks!

> 
> -- 
> All Rights Reversed.