linux-kernel - Re: [RFC][PATCH 00/10] taskstats: Enhancements for precise accounting

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Date:	Mon, 27 Sep 2010 13:02:56 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	holzheu@...ux.vnet.ibm.com
Cc:	Shailabh Nagar <nagar1234@...ibm.com>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...hat.com>,
	John stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	containers@...ts.linux-foundation.org
Subject: Re: [RFC][PATCH 00/10] taskstats: Enhancements for precise
 accounting

On Mon, 27 Sep 2010 11:18:47 +0200
Michael Holzheu <holzheu@...ux.vnet.ibm.com> wrote:

> Hello Andrew,
> 
> On Fri, 2010-09-24 at 11:50 -0700, Andrew Morton wrote:
> > > > This is a big change!  If this is done right then we're heading in the
> > > > direction of deprecating the longstanding way in which userspace
> > > > observes the state of Linux processes and we're recommending that the
> > > > whole world migrate to taskstats.  I think?
> > > 
> > > Or it can be used as alternative. Since procfs has its drawbacks (e.g.
> > > performance) an alternative could be helpful. 
> > 
> > And it can be harmful.  More kernel code to maintain and test, more
> > userspace code to develop, maintain, etc.  Less user testing than if
> > there was a single interface.
> 
> Sure, the value has to be big enough to justify the effort.
> 
> But as I said, with taskstats and procfs we already have two interfaces
> for getting task information.

That doesn't mean it was the right thing to do!  For the reasons I
outline above, it can be the wrong thing to do and strengthening one of
the alternatives worsens the problem.

> Currently in procfs there is information
> than you can't find in taskstats. But also the other way round in the
> taskstats structure there is very useful information that you can't get
> under proc. E.g. the task delay times, IO accounting, etc.

Sounds like a big screwup ;)

Look at it this way: if you were going to sit down and start to design
a new operating system from scratch, would you design the task status
reporting system as it currently stands in Linux?  Don't think so!

> So currently
> tools have to use both interfaces to get all information, which is not
> optimal.
> 
> > > 
> > > > I worry that there's a dependency on CONFIG_NET?  If so then that's a
> > > > big problem because in N years time, 99% of the world will be using
> > > > taskstats, but a few embedded losers will be stuck using (and having to
> > > > support) the old tools.
> > > 
> > > Sure, but if we could add the /proc/taskstats approach, this dependency
> > > would not be there.
> > 
> > So why do we need to present the same info over netlink?
> 
> Good point. It is not really necessary. I started development using the
> netlink code. Therefore I first added the new command in the netlink
> code. I also thought, it would be a good idea to provide all netlink
> commands over the procfs interface to be consistent.

Maybe we should have delivered taskstats over procfs from day one.

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