Re: [Ksummit-2008-discuss] DTrace

From: "J. Bruce Fields" <bfields@fieldses.org>
To: Theodore Tso <tytso@mit.edu>, Roland McGrath <roland@redhat.com>,
		ksummit-2008-discuss@lists.linux-foundation.org,
		systemtap@sources.redhat.com
Subject: Re: [Ksummit-2008-discuss] DTrace
Date: Wed, 02 Jul 2008 20:17:00 -0000	[thread overview]
Message-ID: <20080702201637.GL17296@fieldses.org> (raw)
In-Reply-To: <20080702200650.GJ29916@mail.oracle.com>

On Wed, Jul 02, 2008 at 01:06:51PM -0700, Joel Becker wrote:
> On Tue, Jul 01, 2008 at 07:13:27PM -0400, Theodore Tso wrote:
> > And remember, for the average kernel developer, the question is
> > whether using SystemTap is easier than inserting a bunch of printk's
> 
> 	I'll throw in a datapoint here.  I recently had to track a
> problem down on a distro kernel, and rebuilding distro kernels takes a
> lot of time.  So I decided to try SystemTap.  Once I'd discovered the
> magic location of the distro's debuginfo package, systemtap was *WAY*
> faster than prink+recompile.  I mean, we're talking 30 second turnaround
> between "Oh, I'd like to print this other value" and actually printing
> it.  In the core kernel, not a module.  No reboot, no nothin.  This is a
> huge win.
> 	But I'll never replicate that for my normal work at this rate.
> I'm usually floating multiple hand-built mainline kernels with new
> work.  Just like Ted describes.
> 
> > repository or weekly automated snapshots.)  So actually, being able to
> > install stripped modules and vmlinux into /boot and /linux, and then
> > being able to put the unstripped binaries somewhere else, without
> > having to use the !@#@! complicated RPM macros by Fedora/RHEL is
> > actually **very** important to me.
> 
> 	Me too.  I want to be able to say "make install; make
> tap_install" in my kernel objdir.  "install" does what it always has
> done - no change.  "tap_install" (or whatever) drops things in eg
> /lib/modules/<version>/debug such that systemtap Just Works.

That would be nice.  But I'm afraid I normally don't even have access to
the kernel tree on the machine I'm installing to--I usually build a
monolithic kernel and then scp it to the test machines.  Is there hope
for me?

--b.

> It can
> error if systemtap isn't installed or is too old.  But I shouldn't have
> to build a distro package of my kernel, or even understand the
> mechanism for building 'debuginfo' bits (even if I do).
> 
> Joel
> 
> -- 
> 
> "I am working for the time when unqualified blacks, browns, and
>  women join the unqualified men in running our overnment."
> 	- Sissy Farenthold
> 
> Joel Becker
> Principal Software Developer
> Oracle
> E-mail: joel.becker@oracle.com
> Phone: (650) 506-8127
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