Re: [GIT PULL] Performance Counters for Linux

Ingo Molnar
2009-06-11T20:24:17Z

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

[...]
> 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.

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.

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/.

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

- No one will put getopt.h into the code

- No one will rewrite it in some weird language

[ Or at least, even though such incidents might happen
occasionally, i can just sit back in my chair and watch the
resulting showdown on lkml, without having to worry about the
outcome ;-) ]

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

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?

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.

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.

Ingo