Date: Wed, 17 Dec 2014 13:47:30 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Fengguang Wu <fengguang.wu@intel.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        "Pan, Jacob jun" <jacob.jun.pan@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, LKP <lkp@01.org>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [nohz] 2a16fc93d2c: kernel lockup on idle injection
Message-ID: <20141217124724.GB20739@lerouge>
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 <548FFD20.1040102@linux.vnet.ibm.com>
 <alpine.DEB.2.11.1412161105470.17382@nanos>
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On Wed, Dec 17, 2014 at 10:11:58AM +0100, Thomas Gleixner wrote:
> On Wed, 17 Dec 2014, Frederic Weisbecker wrote:
> > On Tue, Dec 16, 2014 at 10:21:27PM +0100, Thomas Gleixner wrote:
> > > So instead of evaluating the whole nonsense a gazillion times in a row
> > > and firing pointless self ipis why are you not looking at the obvious
> > > solution of sane state change tracking?
> > 
> > Because I had to do it wrong first before somebody like you with a fresh mind
> > comes, look at the whole picture and propose a rethink :-)
> 
> Point taken.
>  
> > >     I told all of you from the very beginning that remote accounting
> > >     is a key mechanism for this, but you keep insisting on hacking
> > >     around it.
> > 
> > I don't, and I think everybody has understood we are not going to accept
> > hacks to solve the 1hz issue.
> 
> You wish.
> 
> > I'm pretty sure you know what this is about to maintain a project with a
> > (variably) cruel lack of manpower ;-)
> 
> Oh yes! :(
>  
> > Moreover I'm not the kind of kernel developer who ignores reviews (whether pre or
> > post merge).
> 
> I know that.
>  
> > So, no point in threatening a dependency to BROKEN or ripping out except perhaps to
> > push me out to other projects with more thankful managers.
> 
> This was not directed to you, really.
> 
> This was directed at the folks who randomly "fix" that code by voodoo
> bandaids instead of analyzing the root causes in the first
> place. You're the least one to blame for that.

Well I was about to propose a bad fix for powerclamp and I sometimes take
overengineering directions. I'm still to blame for several things 8-)

Sorry I got too touchy :-)

Anyway, I'll give a try to your proposition. Somehow I have always felt that
something was wrong with this tick_nohz_can_stop_tick() called all over the place,
that plus the IPI that's often near the scheduler IPI.

I'm pretty sure this is going to help fixing some overhead issues I got reported.

Thanks a lot!
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