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

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Date:	Mon, 18 Sep 2006 10:15:55 +0200
From:	Jes Sorensen <jes@....com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
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

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.

Jes
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