Task profiling in Linux

Task profiling in Linux

[Claudio Scordino]

Hi all.

I need some help to make profiling of an application on Linux. I need to 
measure the computation time between different points of my program, 
considering only the CPU time that the task has actually executed (i.e. 
without the intervals of time that the task has been preempted by other 
tasks).

To accomplish that, I can't just read the current time in different parts of 
the program, nor I can set and use a timer, because this wouldn't consider 
preemptions...

I found out that Linux provides the getrusage() syscall which provides the 
information that I need. This syscall also says both user and system times 
used by the task, which is a very useful thing.

However, it has two main drawbacks:

- its precision is very low: I'm working with real-time tasks on a Athlon-64  
and I need a more accurate estimation

- it can't be invoked by a generic task to know the execution time of another 
task

The only idea that I had is to insert some hooks in the kernel functions and 
use some high resolution timer to compute the time that my task has 
actually executed. This timer starts whenever the task obtains the CPU, and is 
stopped whenever the task yields the CPU.

Therefore, I just need to know which functions are invoked when a task starts  
executing on the CPU and when it looses the CPU.

May somebody tell me which are those functions ?

If somebody has suggestions about how doing this profiling, let me know. 

Many thanks,

            Claudio

Re: Task profiling in Linux

[Jon Masters]

On 10/23/05, Claudio Scordino <cloud.of.andor@gmail.com> wrote:

> I need some help to make profiling of an application on Linux.

Did you already try gprof?

Jon.

Re: Task profiling in Linux

[Benoit Boissinot]

On 10/24/05, Jon Masters <jonmasters@gmail.com> wrote:
> On 10/23/05, Claudio Scordino <cloud.of.andor@gmail.com> wrote:
>
> > I need some help to make profiling of an application on Linux.
>
> Did you already try gprof?
>
or oprofile/sysprof with a recent kernel

Benoit

Re: Task profiling in Linux

[Peter Chubb]

>>>>> "Claudio" == Claudio Scordino <cloud.of.andor@gmail.com> writes:


Claudio> I found out that Linux provides the getrusage() syscall which
Claudio> provides the information that I need. This syscall also says
Claudio> both user and system times used by the task, which is a very
Claudio> useful thing.

Claudio> However, it has two main drawbacks:

Claudio> - its precision is very low: I'm working with real-time tasks
Claudio> on a Athlon-64 and I need a more accurate estimation

Claudio> - it can't be invoked by a generic task to know the execution
Claudio> time of another task

This is part of what my microstate accounting package provides
.... but I haven't done a port to AMD64 yet...

See http://www.gelato.unsw.edu.au/patches/

-- 
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
The technical we do immediately,  the political takes *forever*

Re: Task profiling in Linux

[Claudio Scordino]

Thank you for your suggestion, but I still have a question about it. 

If I do

clock_gettime (CLOCK_THREAD_CPUTIME_ID, &old);
sleep(5);
clock_gettime (CLOCK_THREAD_CPUTIME_ID, &new);

why the difference (new-old) includes also the time the process has slept ?

Maybe there was a misunderstanding: I am looking for a way to know how long a 
process has _actually_ executed, accounting for all periods that it has not 
executed for some reason (like sleep, blocking, preemptions, etc.). And I 
need the high precision gave by the TSC (jiffies is not enough).

getrusage works fine, but has a coarse-grain precision (jiffies).
clock_gettime, instead, has a very good precision (thanks to TSC) but as you 
can see, it does not return the time that the process has actually 
executed...

If I am wrong, please tell me where.

Thank you,

            Claudio


On Monday 31 October 2005 18:15, you wrote:
> On 10/23/05, Claudio Scordino <cloud.of.andor@gmail.com> wrote:
> > To accomplish that, I can't just read the current time in different parts
> > of the program, nor I can set and use a timer, because this wouldn't
> > consider preemptions...
>
> struct timespec start;
> clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &start);
>
> ... do work...
>
> struct timespec end;
> clock_gettime (CLOCK_PROCESS_CPUTIME_ID, &end);
>
> ... subtract start from end
>
> Or use CLOCK_THREAD_CPUTIME_ID if this is more correct for your
> application.
>
> This works since Roland's clock work got added in the 2.6 series.
> Before that preemption wasn't excluded.