linux-kernel - Re: [PATCH] tick/broadcast: Remove redundant code in tick_check_new

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Date:   Tue, 14 Nov 2017 12:39:59 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>
cc:     mingo@...nel.org, fweisbec@...il.com,
        Srinivas REDDY Eeda <srinivas.eeda@...cle.com>,
        Joe Jin <joe.jin@...cle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tick/broadcast: Remove redundant code in
 tick_check_new_device()

On Tue, 14 Nov 2017, Zhenzhong Duan wrote:
> On 2017/11/14 0:54, Thomas Gleixner wrote:
> 
> > On Wed, 8 Nov 2017, Zhenzhong Duan wrote:
> > 
> > > There is no way a timer used as broadcast clockevent device is also used
> > > as
> > > percpu tick clockevent device currently.
> > Correct.
> > 
> > > It's better to put related code in tick_install_broadcast_device(), but I
> > > feel
> > > it's harmless to give it back to the clockevents layer. Pls correct me if
> > > I'm
> > > wrong.
> > You already established, that it _cannot_ be the broadcast device and the
> > per cpu device at the same time. So that condition can never be true. What
> > do you want to put into tick_install_broadcast_device()? This second
> > paragraph doesn't make sense, unless I'm missing something.
> 
> I didn't find the reason in long history logs while the comments saying 'If
> the current device is the broadcast device, do not give it back to the
> clockevents layer !'

To be honest I can't figure it out myself why this was put there, even if I
wrote it myself. Fact is that this is wrong and cannot happen at all.

Thanks,

	tglx