linux-kernel - Re: [patch] Performance Counters for Linux, v3

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Date:	Sun, 14 Dec 2008 23:37:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, eranian@...il.com,
	Vince Weaver <vince@...ter.net>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	Robert Richter <robert.richter@....com>,
	Arjan van de Veen <arjan@...radead.org>,
	Peter Anvin <hpa@...or.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [patch] Performance Counters for Linux, v3


* Paul Mackerras <paulus@...ba.org> wrote:

> Peter Zijlstra writes:
> 
> > On Fri, 2008-12-12 at 18:42 +0100, stephane eranian wrote:
> > > In fact, I know tools which do not even need a library. 
> > 
> > By your own saying, the problem solved by libperfmon is a hard problem
> > (and I fully understand that).
> > 
> > Now you say there is software out there that doesn't use libperfmon,
> > that means they'll have to duplicate that functionality.
> > 
> > And only commercial software has a clear gain by wastefully duplicating
> > that effort. This means there is an active commercial interest to not
> > make perfmon the best technical solution there is, which is contrary to
> > the very thing Linux is about.
> > 
> > What is worse, you defend that:
> > 
> > > Go ask end-users what they think of that?
> > > 
> > > You don't even need a library. All of this could be integrated into the tool.
> > > New processor, just go download the updated version of the tool.
> > 
> > No! what people want is their problem fixed - no matter how. That is one
> > of the powers of FOSS, you can fix your problems in any way suitable.
> > 
> > Would it not be much better if those folks duped into using a binary
> > only product only had to upgrade their FOSS kernel, instead of possibly
> > forking over more $$$ for an upgrade?
> > 
> > You have just irrevocably proven to me this needs to go into the kernel,
> > as the design of perfmon is little more than a GPL circumvention device
> > - independent of whether you are aware of that or not.
> 
> I'm sorry, but that is a pretty silly argument.
> 
> By that logic, the kernel module loader should include an in-kernel copy 
> of gcc and binutils, and the fact that it doesn't proves that the module 
> loader is little more than a GPL circumvention device - independent of 
> whether you are aware of that or not.  8-)

i'm not sure how your example applies: the kernel module loader is not an 
application that needs to be updated to new versions of syscalls. Nor is 
it a needless duplication of infrastructure - it runs in a completely 
different protection domain - just to name one of the key differences.

Applications going to complex raw syscalls and avoiding a neutral hw 
infrastructure library that implements a non-trivial job is quite typical 
for FOSS-library-shy bin-only apps. The "you cannot infringe what you do 
not link to at all" kind of defensive thinking.

	Ingo
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