linux-kernel - Re: Performance analysis of Linux Kernel Markers 0.20 for 2.6.17

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Date:	Sat, 30 Sep 2006 23:42:12 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Nicholas Miell <nmiell@...cast.net>
Cc:	Martin Bligh <mbligh@...gle.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	prasanna@...ibm.com, Andrew Morton <akpm@...l.org>,
	Ingo Molnar <mingo@...e.hu>, Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jes Sorensen <jes@....com>, Tom Zanussi <zanussi@...ibm.com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	Christoph Hellwig <hch@...radead.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	William Cohen <wcohen@...hat.com>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Karim Yaghmour <karim@...rsys.com>,
	Pavel Machek <pavel@...e.cz>, Joe Perches <joe@...ches.com>,
	"Randy.Dunlap" <rdunlap@...otime.net>,
	"Jose R. Santos" <jrs@...ibm.com>
Subject: Re: Performance analysis of Linux Kernel Markers 0.20 for 2.6.17

* Nicholas Miell (nmiell@...cast.net) wrote:
> On Sat, 2006-09-30 at 14:01 -0400, Mathieu Desnoyers wrote:
> > Hi,
> > 
> > Following the huge discussion thread about tracing/static vs dynamic
> > instrumentation/markers, a consensus seems to emerge about the need for a
> > marker system in the Linux kernel. The main issues this mechanism addresses are:
> > 
> > - Identify code important to runtime data collection/analysis tools in tree so
> >   that it follows the code changes naturally.
> > - Be visually appealing to kernel developers.
> > - Have a very low impact on the system performance.
> > - Integrate in the standard kernel infrastructure : use C and loadable modules.
> > 
> > The time has come for some performance measurements of the Linux Kernel Markers,
> > which follows. I attach a PDF with tables and charts which condense these
> > results.
> 
> Has anyone done any performance measurements with the "regular function
> call replaced by a NOP" type of marker?
> 

Here it is (on the same setup as the other tests : Pentium 4, 3 GHz) :

* Execute an empty loop

- Without marker
NR_LOOPS : 10000000
time delta (cycles): 15026497
cycles per loop : 1.50

- With 5 NOPs
NR_LOOPS : 100000
time delta (cycles): 300157
cycles per loop : 3.00
added cycles per loop for nops : 3.00-1.50 = 1.50


* Execute a loop of memcpy 4096 bytes

- Without marker
NR_LOOPS : 10000
time delta (cycles): 12981555
cycles per loop : 1298.16

- With 5 NOPs
NR_LOOPS : 10000
time delta (cycles): 12983925
cycles per loop : 1298.39
added cycles per loop for nops : 0.23


If we compare this approach to the jump-over-call markers (in cycles per loop) :

              NOPs    Jump over call generic    Jump over call optimized
empty loop    1.50    1.17                      2.50 
memcpy        0.23    2.12                      0.07



Mathieu


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