timing an application

timing an application

[Maciej Soltysiak]

Hi,

being inspired by some book about optimizing c++ code i decided to do
timing of functions i wrote. I am using gettimeofday to set
two timeval structs and calculate the time between them.
But the results depend heavily on the load, also i reckon that this
is an innacurate timing.

Any ideas on timing a function, or a block of code? Maybe some kernel
timers or something.

Regards,
Maciej Soltysiak

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Re: timing an application

[Chris Friesen]

Maciej Soltysiak wrote:
> Hi,
> 
> being inspired by some book about optimizing c++ code i decided to do
> timing of functions i wrote. I am using gettimeofday to set
> two timeval structs and calculate the time between them.
> But the results depend heavily on the load, also i reckon that this
> is an innacurate timing.
> 
> Any ideas on timing a function, or a block of code? Maybe some kernel
> timers or something.

gettimeofday() is accurate.  However, your task may be interrupted by
other tasks, interrupts, etc.

Your best bet may be to do many iterations of the routine in question and then
do some statistical analysis of the results.

Chris



-- 
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Re: timing an application

[Corey Minyard]

I have a patch at http://home.attbi.com/~minyard/highres-2.4.17.patch that
adds a config item that times CPU usage at microsecond resolution.  It's 
only
for the 2.4.17 kernel, I don't know what the porting effort would be for 
other
kernels.

It's not a great patch, it would need some work to be really clean from 
a code
quality point of view, but it does seem to work.  With it you can use 
getrusage()
to get the actual time your process has used between two points.  It 
works on
x86 and PPC.

Plus, obviously, this adds significant time to system calls and interrupts.

-Corey

Chris Friesen wrote:

> Maciej Soltysiak wrote:
>
>> Hi,
>>
>> being inspired by some book about optimizing c++ code i decided to do
>> timing of functions i wrote. I am using gettimeofday to set
>> two timeval structs and calculate the time between them.
>> But the results depend heavily on the load, also i reckon that this
>> is an innacurate timing.
>>
>> Any ideas on timing a function, or a block of code? Maybe some kernel
>> timers or something.
>
>
> gettimeofday() is accurate.  However, your task may be interrupted by
> other tasks, interrupts, etc.
>
> Your best bet may be to do many iterations of the routine in question 
> and then
> do some statistical analysis of the results.
>
> Chris
>
>
>

Re: timing an application

[Richard B. Johnson]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 978 bytes --]

On Tue, 14 Jan 2003, Maciej Soltysiak wrote:

> Hi,
> 
> being inspired by some book about optimizing c++ code i decided to do
> timing of functions i wrote. I am using gettimeofday to set
> two timeval structs and calculate the time between them.
> But the results depend heavily on the load, also i reckon that this
> is an innacurate timing.
> 
> Any ideas on timing a function, or a block of code? Maybe some kernel
> timers or something.
> 
> Regards,
> Maciej Soltysiak
> 

Easy!  Use the rdtsc instruction to obtain the number of CPU cycles
that occur between two subsequent calls. There will be some 'noise'
because of interrupt activity so make many tests, put the results
into an array, remove the slowest and the fastest, then average
the remaining data. That's good enough for "government projects".

Cheers,
Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.


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Re: timing an application [results]

[Maciej Soltysiak]

Thanks for all your input on this.

I am using rdtsc, works great.
But a funny thing happens.
Here are the results for a block of code that counts the number players
who are fighting: (in a mud)

A) Pentium II 350, 2.4.20-grsec
about 700us with 250k CPU cycles

B) Pentium IV 1,5 ghz 2.4.20-lowlatency-preemt-aa
about 800us with 130k CPU cycles.

Maybe it is because the patches, but it seems that P4 does the same
longer but with less CPU cycles. Could that be correct?
Maybe something there is inacurate?

Regards,
Maciej Soltysiak

Re: timing an application

[Olaf Dietsche]

Maciej Soltysiak <solt@dns.toxicfilms.tv> writes:

> being inspired by some book about optimizing c++ code i decided to do
> timing of functions i wrote. I am using gettimeofday to set
> two timeval structs and calculate the time between them.
> But the results depend heavily on the load, also i reckon that this
> is an innacurate timing.

You will get elapsed time, which is usually not the same as used cpu
time.

> Any ideas on timing a function, or a block of code? Maybe some kernel
> timers or something.

If you're timing/pofiling some user space functions, gprof should be
sufficient. If you want to profile kernel and module functions as
well, try oprofile at <http://oprofile.sourceforge.net/>. It is part
of the kernel since 2.5.43.

Regards, Olaf.

RE: timing an application

[Howell, David P]

If this is on a IA32(Pentium II or later)/IA64 have you considered using
the processor TSC register to get interval timestamps? It's a lot
lighter weight and should give better resolution. When we have done this
we compared the tick values directly.

To convert TSC ticks to time the /proc/cpuinfo value for 'cpu MHz', see
the glibc get_clockfreq.c and hp_timing.h implementation for details.

Dave Howell

-----Original Message-----
From: Maciej Soltysiak [mailto:solt@dns.toxicfilms.tv] 
Sent: Tuesday, January 14, 2003 2:58 PM
To: linux-kernel@vger.kernel.org
Subject: timing an application

Hi,

being inspired by some book about optimizing c++ code i decided to do
timing of functions i wrote. I am using gettimeofday to set
two timeval structs and calculate the time between them.
But the results depend heavily on the load, also i reckon that this
is an innacurate timing.

Any ideas on timing a function, or a block of code? Maybe some kernel
timers or something.

Regards,
Maciej Soltysiak

-----BEGIN GEEK CODE BLOCK-----
VERSION: 3.1
GIT/MU d-- s:- a-- C++ UL++++$ P L++++ E- W- N- K- w--- O! M- V- PS+
PE++
Y+ PGP- t+ 5-- X+ R tv- b DI+ D---- G e++>+++ h! y?
-----END GEEK CODE BLOCK-----
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RE: timing an application

[David Mosberger]

>>>>> On Tue, 14 Jan 2003 12:37:05 -0800, "Howell, David P" <david.p.howell@intel.com> said:

  Dave> If this is on a IA32(Pentium II or later)/IA64 have you
  Dave> considered using the processor TSC register to get interval
  Dave> timestamps? It's a lot lighter weight and should give better
  Dave> resolution. When we have done this we compared the tick values
  Dave> directly.

  Dave> To convert TSC ticks to time the /proc/cpuinfo value for 'cpu
  Dave> MHz', see the glibc get_clockfreq.c and hp_timing.h
  Dave> implementation for details.

Note that it's tricky to uses TSC/ITC on multiprocessors, especially
on large machines, on which the clocks for different CPUs may drift, etc.
It's much better to use the clock_gettime() routine:

  http://www.opengroup.org/onlinepubs/007908799/xsh/clock_getres.html

Where properly implemented, this will be both as fast and accurate.

	--david