Re: Performance analysis of Linux Kernel Markers 0.20 for 2.6.17

[Mathieu Desnoyers <compudj@krystal.dyndns.org>]

* Nicholas Miell (nmiell@comcast.net) wrote:
> On Sat, 2006-09-30 at 23:42 -0400, Mathieu Desnoyers wrote:
> > * Nicholas Miell (nmiell@comcast.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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