Date:	Thu, 11 Jun 2009 22:49:17 +0200
From:	Marcel Holtmann <marcel@...tmann.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Al Viro <viro@...iv.linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Stephane Eranian <eranian@...glemail.com>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [GIT PULL] Performance Counters for Linux

Hi Ingo,

> > What the "keep it in the kernel sources" approach hopefully allows is
> > 
> >  - taking advantage of new features in a timely manner.
> > 
> >    NOT with some ABI breakage, but simply things like supporting a 
> >    new CPU architecture or new counters. The thing that oprofile 
> >    failed at so badly in my experience.
> >
> >  - Make it easier for developers, and _avoiding_ the horrible 
> >    situation where you have two different groups that don't talk 
> >    well to each other because one is a group of user-space 
> >    weenies, and the other is a group of manly kernel people, and 
> >    there is no common ground.
> 
> Yes, very much agreed.
> 
> Btw., here are a couple of other arguments why i find it useful to 
> have the tools/perf/ in the kernel repo:
> 
> 1) Super-fast and synchronized release cycles
> 
> The kernel is one of the fastest moving packages in Linux - most 
> user-space packages have (much!) longer release cycles than 3 
> months.

that might be true for some projects, but for others this is wrong. You
are just making an assumption out of thin air.

> A tight release schedule forces a certain amount of release 
> discipline on tooling as well - so i'm glad that the two will be 
> coupled. It's so easy for a promising tool to degrade into 
> tinkerware with odd release cycles with time - if it's part of the 
> kernel then at least the release cycles wont be odd but at precise 3 
> months.

And you can't do that within a perf.git tree on kernel.org because?

> 2) Performance _matters_
> 
> This is an argument pretty specific to perfcounters: Performance 
> analysis tools under Linux suck pretty summarily. Yet, one of the 
> major strengths of Linux is (or at least used to be) performance. So 
> i find it very fitting that the kernel community takes performance 
> analysis tooling into their own hand.
> 
> 3) Strict quality control under a proven mode
> 
> In the kernel repo i can be sure that:
> 
>   - No one will even think of adding autofools to tools/perf/.

That argument is non-sense. While autoconf/automake is maybe not to your
liking, nobody forces you to use it. Projects like git, iw etc. do
perfectly fine without it. I don't mind having autoconf/automake around.

>   - No one will send us code with Hungarian notation and two spaces
>     tabulation.

What kind of shitty argument it is that. I enforce kernel coding style
in my userspace project all the time. No problem with that.

>   - No one will put getopt.h into the code

And that is so bad because?

>   - No one will rewrite it in some weird language

And they can do as they please. You don't have to accept the re-write.
These are all non-sense arguments. If you maintain a userspace project
properly then you will not see any of these problems.

> I can point contributors to well-established kernel coding 
> principles, without having to argue no end about them.

Come on. A lot of projects use kernel coding style nowadays. That is not
a problem here.

> All in one - the Linux kernel is a fire breathing monster engine 
> when it comes to producing good software. Who says it that that this 
> infrastructure and experience can only be used to produce kernel 
> space code?

And who says that all userspace people have no idea what they are doing.
We have a lot of successful project that follow almost the same rules as
the kernel.

> 4) Code reuse
> 
> We actually use code from the kernel: list.h primitives and 
> rbtrees.c. We privatized them for now under 
> tools/perf/util/rbtree.[ch] and tools/perf/util/list.h because 
> there's some header and type pollution in them, but it would be nice 
> to include them directly and share the facilities.

Lets see if you are making up an argument or if you are really trying to
work this out and solve it.

> 5) Reality check for kernel developers
> 
> I think kernel hackers need a reality check too. It's easy to say 
> that user-space sucks - but now there's a way and channel that 
> frustration via direct action and make a real difference. I do hope 
> that the extra superfluous mental energies visible in this thread 
> can be used for good purposes too ;-)
> 
> 6) It's a lot of fun
> 
> I never thought i'd say that - but hacking properly structured 
> user-space code in the kernel repo is serious fun. It's even 
> relaxing at times: i can be reasonably sure that i wont crash the 
> kernel.
> 
> All in one, we did this because we found that it produces better 
> code in practice and does it faster - and i dont think we should 
> rigidly limit the kernel repo to kernel-space projects alone.

Linus has a bad expierience with oprofile and wants to try something new
and I can follow that argument to a certain degree. I don't agree with
it, but that is fine.

So you are saying that only good code comes from including it into
linux-2.6.git and otherwise you will never get there. Have you actually
tried to maintain this in a separate repository on kernel.org?

Regards

Marcel


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