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

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Date:	Sun, 1 Oct 2006 11:33:17 -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 23:42 -0400, Mathieu Desnoyers wrote:
> > * Nicholas Miell (nmiell@...cast.net) wrote:
> > > 
> > > 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
> 
> What about with two NOPs (".byte 0x66, 0x66, 0x90, 0x66, 0x90" - this
> should work with everything) or one (".byte 0x0f, 0x1f, 0x44, 0x00,
> 0x00" - AFAIK, this should work with P6 or newer).
> 
> (Sorry, I should have mentioned this the first time.)
> 

Hi,

The tests I made were with : 
#define GENERIC_NOP1    ".byte 0x90\n"
#define GENERIC_NOP4        ".byte 0x8d,0x74,0x26,0x00\n"
#define GENERIC_NOP5        GENERIC_NOP1 GENERIC_NOP4

Now with the tests you ask for :

* Execute an empty loop
- 2 NOPs ".byte 0x66, 0x66, 0x90, 0x66, 0x90"
NR_LOOPS : 100000
time delta (cycles): 200190
cycles per loop : 2.00
cycles per loop for nops : 2.00-1.50 = 0.50

- 1 NOP "0x0f, 0x1f, 0x44, 0x00, 0x00"
NR_LOOPS : 100000
time delta (cycles): 300172
cycles per loop : 3.00
cycles per loop for nops : 3.00-1.50 = 2.50


* Execute a loop of memcpy 4096 bytes
- 2 NOPs ".byte 0x66, 0x66, 0x90, 0x66, 0x90"
NR_LOOPS : 10000
time delta (cycles): 12981293
cycles per loop : 1298.13
cycles per loop for nops : 1298.16-1298.13=0.03

- 1 NOP "0x0f, 0x1f, 0x44, 0x00, 0x00"
NR_LOOPS : 10000
time delta (cycles): 12985590
cycles per loop : 1298.56
cycles per loop for nops : 0.43


Mathieu


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