Re: [RFC][PATCH 0/5] NFS: trace points added to mounting path

[Arnaldo Carvalho de Melo <acme at redhat dot com>]

Em Wed, Jan 21, 2009 at 11:39:56AM -0500, Steve Dickson escreveu:
> K.Prasad wrote:
> > On Mon, Jan 19, 2009 at 09:27:30AM -0500, Jeff Moyer wrote:
> >> Greg Banks <gnb@melbourne.sgi.com> writes:
> >>
> >>> Steve Dickson wrote:
> >>>> So the ultimate goal would be to replace all the dprintks with trace points
> >>>> but still be able to enable them through the rpcdebug command
> >>> I have a patch which changes the definition of the dprintk() macro (but
> >>> *not* dprintk() callsites) to allow enabling and disabling individual
> >>> dprintk() statements through a /proc/ interface.  Would you be
> >>> interested in that?
> >> That sounds like duplicated work.  How does it differ from Jason Baron's
> >> dynamic printk patches (which I believe are now upstream)?
> >>
> >> Cheers,
> >> Jeff
> > 
> > Introducing/converting one of the accepted methods of static
> > instrumentation - like tracepoints would help more users (whether
> > in-kernel or otherwise) harness them.
> > 
> > Steve,
> > 	Would it help convert the systemtap script (nfs_mount.stp) in
> > Patch - 5 into a kernel module (perhaps in samples/ directory) to bring
> > an in-kernel user of these tracepoints?
> Well nfs_mount.stp was just an example of how to pull the information
> from the kernel.. I just wanted to complete the loop... but as 
> Christoph pointed out it probably shouldn't been included in the posting.
> 
> I'm not sure moving the nfs_mount.stp script into kernel 
> would make sense. One of the advantages of trace point and system
> scripts (depending on what is passed up) it allows users to define
> exactly what they need to see.. 
> 
> For example, a kernel guy might be interested in a particular bit in a flag 
> field which would be meaningless to an IT guy. On the other hand, the IT guy 
> would be interested in the error code. One trace point could supply all the
> information but different systemtap scripts would be need to show the 
> desired information.
> 
> My point being, if we move things down into the kernel, I think we would
> lose this type of flexibly...

I suggest you provide an ftrace plugin, just like I'm doing with
blktrace, see:

http://lkml.org/lkml/2009/1/20/190

- Arnaldo