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

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Date:	Tue, 15 Apr 2008 15:17:44 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	prasad@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, Christoph Hellwig <hch@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [RFC PATCH 1/2] Marker probes in futex.c


* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> > Because we extract the field names and types, we can create tracer 
> > plugins that would hook on field names rather than expect a specific 
> > number of fields and fixed field types. It makes it possible to 
> > tolerate missing fields pretty easily. But yes, tracer tools might 
> > have to be adapted to internal kernel changes, since they must 
> > follow kernel structure changes. However, staying as close as 
> > possible to a canonical representation of event fields, staying far 
> > from the specific implemetation, would help to lessen the 
> > inter-dependency. On the other hand, it would probably hurt trace 
> > compactness and efficiency.
> 
> See, these tracer tools are my nightmare as member of an enterprise 
> linux team. They'll make an already hard job even harder, no thanks!

i'm clearly NAK-ing all futex trace hooks until the true impact of the 
whole marker facility is better understood. I've tried them for the 
scheduler and they were a clear failure: too bloated and too persistent.

but more importantly, as things stand today i've yet to see a _any_ 
bugreport where these 'tracer' tools that are being referred to were 
actually used in the field to fix something. The latency tracers (and 
the other tracer variants in -rt) on the other hand have a documented 
track record of being useful in fixing bugs and instrumenting the 
kernel.

	Ingo
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