linux-kernel - Re: nohz: remove nohz_cpu

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Message-ID: <1311036800.27358.26.camel@debian>
Date:	Tue, 19 Jul 2011 08:53:20 +0800
From:	"Alex,Shi" <alex.shi@...el.com>
To:	"tglx@...utronix.de" <tglx@...utronix.de>
Cc:	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Fu, Michael" <michael.fu@...el.com>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>
Subject: Re: nohz: remove nohz_cpu_mask

Thomas: 

Maybe you omit this thread, So I ping you again. :) 
What's your opinion of this patch? I will be glad to hear from you for
any messages. 

Regards!
Alex 
On Fri, 2011-07-15 at 08:51 +0800, Alex,Shi wrote:
> On Tue, 2011-07-12 at 01:30 +0800, Paul E. McKenney wrote:
> > On Mon, Jul 11, 2011 at 08:47:05AM +0800, Alex,Shi wrote:
> > > RCU didn't use this global variable now. Currently no user on it.
> > 
> > Indeed.  RCU's use of it turned out to be quite buggy.  :-(
> > 
> > > Since the ts->do_timer_last is not the real last periodic tick cpu in
> > > most of time. I once want to compare the cpu_online_mask and
> > > nohz_cpu_mask to get a real one, and than only let that cpu sleep
> > > shorter, other cpu will try to sleep KTIME_MAX, that need a extra lock
> > > for nohz_cpu_mask. But I checked my all platforms, from NHM-EX server to
> > > laptops, all of them are waked up a few times per second. So, the
> > > advantage is only in theory. 
> > > 
> > > Since no clear usage of this variable, why not remove it? That can save
> > > a cache-line in all cpus and reduce atomic sync contention.
> > 
> > Works for me!
> > 
> > Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> 
> Thomas, would you like to give some comments of this? 
> 
> Best regards!
> Alex


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