linux-kernel - Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

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Date:	Mon, 18 Sep 2006 10:53:35 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Jes Sorensen <jes@....com>
Cc:	Ingo Molnar <mingo@...e.hu>, Roman Zippel <zippel@...ux-m68k.org>,
	Andrew Morton <akpm@...l.org>, tglx@...utronix.de,
	karim@...rsys.com, Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Tom Zanussi <zanussi@...ibm.com>, ltt-dev@...fik.org,
	Michel Dagenais <michel.dagenais@...ymtl.ca>
Subject: Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

* Jes Sorensen (jes@....com) wrote:
> Mathieu Desnoyers wrote:
> > And about those extra cycles.. according to :
> > Documentation/kprobes.txt
> > "6. Probe Overhead
> > 
> > On a typical CPU in use in 2005, a kprobe hit takes 0.5 to 1.0
> > microseconds to process.  Specifically, a benchmark that hits the same
> > probepoint repeatedly, firing a simple handler each time, reports 1-2
> > million hits per second, depending on the architecture.  A jprobe or
> > return-probe hit typically takes 50-75% longer than a kprobe hit.
> > When you have a return probe set on a function, adding a kprobe at
> > the entry to that function adds essentially no overhead.
> [snip]
> > So, 1 microsecond seems more like 1500-2000 cycles to me, not 50.
> 
> So call it 2000 cycles, now go measure it in *real* life benchmarks
> and not some artificial I call this one syscall that hits the probe
> every time in a tight loop, kinda thing.
> 
> Show us some *real* numbers please.
> 

You are late (I don't blame you about it, considering the size of this thread).
It has been posted in the following email :

http://linux.derkeiler.com/Mailing-Lists/Kernel/2006-09/msg04492.html

Mathieu


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