linux-kernel - Re: [PATCH v1 5/6] mm: make vmstat

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Date:	Tue, 8 May 2012 18:25:07 +0300
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Tejun Heo <tj@...nel.org>, John Stultz <johnstul@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Mike Frysinger <vapier@...too.org>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Frederic Weisbecker <fweisbec@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH v1 5/6] mm: make vmstat_update periodic run conditional

On Mon, May 7, 2012 at 10:40 PM, Christoph Lameter <cl@...ux.com> wrote:
> On Mon, 7 May 2012, KOSAKI Motohiro wrote:
>
>> > > @@ -1204,8 +1265,14 @@ static int __init setup_vmstat(void)
>> > >
>> > >           register_cpu_notifier(&vmstat_notifier);
>> > >
>> > > + INIT_DELAYED_WORK_DEFERRABLE(&vmstat_monitor_work,
>> > > +                         vmstat_update_monitor);
>> > > + queue_delayed_work(system_unbound_wq,
>> > > +                         &vmstat_monitor_work,
>> > > +                         round_jiffies_relative(HZ));
>> > > +
>> > >           for_each_online_cpu(cpu)
>> > > -         start_cpu_timer(cpu);
>> > > +         setup_cpu_timer(cpu);
>> > >   #endif
>> > >   #ifdef CONFIG_PROC_FS
>> > >           proc_create("buddyinfo", S_IRUGO,
>> > > NULL,&fragmentation_file_operations);
>> >
>> > So the monitoring thread just bounces around the system? Hope that the
>> > scheduler does the right thing to keep it on processors that do some other
>> > work.
>>
>> Good point. Usually, all cpus have update items and monitor worker only makes
>> new noise. I think this feature is only useful some hpc case.  So I wonder if
>> this vmstat improvemnt can integrate Frederic's Nohz cpusets activity. I.e.
>> vmstat-update integrate timer house keeping and automatically stop when
>> stopping
>> hz house keeping.
>
> Right. We could do the same processing in vmstat update and the
> thread could check if it is the last vmstat update thread. If so simply
> continue and do not terminate.
>
> But this would still mean that the vmstat update thread would run on an
> arbitrary cpu. If I have a sacrificial lamb processor for OS processing
> then I would expect the vmstat update thread to stick to that processor
> and avoid to run on the other processor that I would like to be as free
> from OS noise as possible.
>

OK, what about -

- We pick a scapegoat cpu (the first to come up gets the job).
- We add a knob to let user designate another cpu for the job.
- If scapegoat cpus goes offline, the cpu processing the off lining is
the new scapegoat.

Does this makes better sense?

Gilad


-- 
Gilad Ben-Yossef
Chief Coffee Drinker
gilad@...yossef.com
Israel Cell: +972-52-8260388
US Cell: +1-973-8260388
http://benyossef.com

"If you take a class in large-scale robotics, can you end up in a
situation where the homework eats your dog?"
 -- Jean-Baptiste Queru
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