linux-kernel - Re: [RFC PATCH 1/2] Marker probes in futex.c

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Date:	Tue, 15 Apr 2008 21:43:49 +0530
From:	"K. Prasad" <prasad@...ux.vnet.ibm.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	prasad@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, mingo@...e.hu,
	Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [RFC PATCH 1/2] Marker probes in futex.c

On Tue, Apr 15, 2008 at 04:50:09PM +0400, Alexey Dobriyan wrote:
> On Tue, Apr 15, 2008 at 08:32:34AM -0400, Mathieu Desnoyers wrote:
> > * Peter Zijlstra (a.p.zijlstra@...llo.nl) wrote:
> > > On Tue, 2008-04-15 at 17:23 +0530, K. Prasad wrote:
> > > 
> > > > +	trace_mark(futex_wait_called, "uaddr:%p fshared:%p val:%u "
> > > > +			"abs_time:%p bitset:%d",
> > > > +			uaddr, fshared, val, abs_time, bitset);
> > > 
> > > This is some seriuosly ugly looking gunk, why would we want stuff like
> > > that scattered across the code?
> > > 
> > 
> > I don't really see how it differs so much from printks, which kernel
> > developers are already familiar with.
> 
> They aren't in every -E codepath, nor they are at the start
> and at the end of every important function (like system call).
> 
> Such printks are usually inserted during debugging when you don't care
> about ugliness and these patches will eventually make kernel looks like
> being permanently debugged one.
>
Wondering how useful would printks be when debugging large systems (say
analysing futex contention on a 32-way CPU system)....also to mention
the inability to do a binary dump of the interested data structures.

--K.Prasad
 
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