linux-kernel - Re: [patch for 2.6.26 0/7] Architecture Independent Markers

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Message-ID: <20080328101500.GF30863@elte.hu>
Date:	Fri, 28 Mar 2008 11:15:00 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	KOSAKI Motohiro <m-kosaki@...es.dti.ne.jp>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [patch for 2.6.26 0/7] Architecture Independent Markers

* KOSAKI Motohiro <m-kosaki@...es.dti.ne.jp> wrote:

> >      text    data     bss     dec     hex filename
> >     37642    7014     384   45040    aff0 sched.o.before
> >     37930    7134     384   45448    b188 sched.o.after
> >
> >  288 bytes for only 3 markers in the scheduler - that's 96 bytes added
> >  per every marker (44 bytes of that in the fastpath).
> >
> >  and the tracer codepath is now slower and more complex as well.
> >
> >  A classic lose-lose situation, so let's apply this patch. Not!
> >
> >  NACK-ed-by: Ingo Molnar <mingo@...e.hu>
> 
> I wonder why nobody doesn't fix this serious problem until now. and I 
> am interesting to what difference to ftrace and marker.

i warned and moaned about it ad nauseum.

furthermore, and because it's Friday again, let me remind folks that 
SystemTap has an even more significant bloat problem: the fact that it 
needs a huge download:

 Installing:
   kernel-debuginfo         x86_64     2.6.25-0.163.rc7.git1.fc9  
   development-debuginfo  198 M
 Installing for dependencies:
   kernel-debuginfo-common  x86_64     2.6.25-0.163.rc7.git1.fc9  
   development-debuginfo   30 M

 Total download size: 229 M

for _every_ updated kernel. That 229 MB size reduces the user base of 
SystemTap (which is otherwise a totally brilliant and cool tool) to 1% 
of its potential userbase, to those truly desperate persons who really 
_need_ to get their problem debugged somehow. But it's nowhere near 
usable as an easy, ad-hoc kernel instrumentation tool, just due to the 
sheer size it brings.

for heaven's sake, we can have 3 years of _full Linux kernel history_, 
with all 87875 commits, with full changelog and dependencies and full 
source code included, packed into a rather tight, 180 MB git repository 
...

[ and then i havent even begun about the on-disk footprint of this 
  monstrum, after the packages have been installed: an additional 850 MB.
  Puh-lease ... ]

there's a huge disconnect with reality here.

	Ingo
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