linux-kernel - Re: vmstat: On demand vmstat workers V5

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Message-ID: <20140529142602.GA20258@localhost.localdomain>
Date:	Thu, 29 May 2014 16:26:05 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Christoph Lameter <cl@...two.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tejun Heo <tj@...nel.org>, John Stultz <johnstul@...ibm.com>,
	Mike Frysinger <vapier@...too.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, hughd@...gle.com,
	viresh.kumar@...aro.org, hpa@...or.com, mingo@...nel.org,
	peterz@...radead.org
Subject: Re: vmstat: On demand vmstat workers V5

On Thu, May 29, 2014 at 09:07:44AM -0500, Christoph Lameter wrote:
> On Thu, 29 May 2014, Frederic Weisbecker wrote:
> 
> > The cpumasks in cpu.c are special as they are the base of the cpumask_var_t
> > definition. They are necessary to define nr_cpu_bits which is the base of
> > cpumask_var_t allocations. As such they must stay lower level and defined
> > on top of NR_CPUS.
> >
> > But most other cases don't need that huge static bitmap. I actually haven't
> > seen any other struct cpumask than isn't based on cpumask_var_t.
> 
> Well yes and I am tying directly into that scheme there in cpu.c to
> display the active vmstat threads in sysfs. so its the same.

I don't think so. Or is there something in vmstat that cpumask_var_t
definition depends upon?

> 
> > Please post it on a new thread so it gets noticed by others.
> 
> Ok. Will do when we got agreement on the cpumask issue.
> 
> I would like to have some way to display the activities on cpus in /sysfs
> like I have done here with the active vmstat workers.
> 
> What I think we need is display cpumasks for
> 
> 1. Cpus where the tick is currently off
> 2. Cpus that have dynticks enabled.
> 3. Cpus that are idle

You should find all that in /proc/timer_list

Now for CPUs that have full dynticks enabled, we probably need something
in sysfs. We could dump the nohz cpumask somewhere. For now you can only grep
the dmesg

> 4. Cpus that are used for RCU.

So, you mean those that aren't in extended grace period (between rcu_user_enter()/exit
or rcu_idle_enter/exit)?

Paul?
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