linux-kernel - Re: [RFC] simple dprobe like markers for the kernel

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Message-ID: <20080710181822.GA20174@redhat.com>
Date:	Thu, 10 Jul 2008 14:18:22 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Theodore Tso <tytso@....edu>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	systemtap@...rceware.org
Subject: Re: [RFC] simple dprobe like markers for the kernel

Hi -

On Thu, Jul 10, 2008 at 11:30:17AM -0400, Theodore Tso wrote:

> [...]  When you said a tool could determine if the tracepoint had
> gotten optimized away, or the variables were no longer present, I
> assume you meant at compile time, right?  So with the right tool
> built into the kbuild infrastructure, if we could simply print
> warnings when tracepoints had gotten optimized away [...]

It will be interesting to see how frequently such a warning appears
for a good suite of such mini markers, on a diversity of architectures
and compilers.  Such data can help pronounce judgement on this approach.


> P.S.  When you said that the current kernel markers are "a bit
> heavyweight", how bad are they in practice?  Hundreds of cycles?  More?

Good question.  The only performance measurements I have seen posted
indicate negligible effects.


- FChE
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