linux-kernel - Re: nohz_full left a periodic tick cpu issue

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Date:	Thu, 12 Dec 2013 08:16:41 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
CC:	Ingo Molnar <mingo@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linaro Kernel <linaro-kernel@...ts.linaro.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>
Subject: Re: nohz_full left a periodic tick cpu issue

On 12/11/2013 11:31 PM, Frederic Weisbecker wrote:
>> > OK, I'll bite...  Why not just use CONFIG_NO_HZ_FULL_SYSIDLE=y with
>> > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL set to at least the number of CPUs on
>> > your system?  The default for CONFIG_NO_HZ_FULL_SYSIDLE_SMALL is eight.
>> > This stuff is in mainline, though Frederic's exploitation of it is
>> > still in the works.
>> > 
>> > On smaller systems, with Frederic's latest work, this should allow CPU 0
>> > to go idle quickly.
>> > 
>> > What are you needing that this would not provide?
> Yeah I think that's what he needs, but we haven't much advertized that feature
> yet. I mean there are good reasons, it's not yet working :o)

Many thanks for Paul and Frederic's comments!

yes, I enabled FULL_SYSIDLE with FULL_SYSIDLE_SMALL=2, but as Frederic
said they are not yet working.

> 
> But yeah Alex, I'm working on plugging the full system idle detection (CONFIG_NO_HZ_FULL_SYSIDLE=y)
> to shutdown the timekeeping CPUs adaptively.
> 
> I have the patches ready, I'm just polishing a few things, writing changelogs, then I'll send
> to LKML with you Cc'ed :)

I am very glad to hear this. looking forward to seeing your patch soon. :)

-- 
Thanks
    Alex
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