looking for a function

looking for a function

[Xu Yang]

Hi guys,

I am looking for a function that can show me the current thread is
running on which cpu.

e.g I am using pthread to write a multithreaded program, in each
thread I would like to insert such kind of function so that I can know
on which cpu this thread is running on.

which function should be used?

thanks for the help!!

best regards,



Yang

Re: looking for a function

[Bernd Petrovitsch]

Hi!

On Tue, 2008-09-16 at 14:50 +0200, Xu Yang wrote:
> Hi guys,
> 
> I am looking for a function that can show me the current thread is
> running on which cpu.

> e.g I am using pthread to write a multithreaded program, in each
> thread I would like to insert such kind of function so that I can know
> on which cpu this thread is running on.

That doesn't make much sense as the same thread can run on a different
CPU after each scheduling decision. And - as it is in userspace -
scheduling can happen before any assembler op.

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services

Re: looking for a function

[Xu Yang]

Hi Bernd,

thanks for you reply.

yes, I know the thread migrates all the time, this is exactly what I
would like to observe. I would like to learn about the thread
migration of some specific scheduling algorithm. so ....

any idea about the function?

Best regards,

Yang

2008/9/16, Bernd Petrovitsch <bernd@firmix.at>:
> Hi!
>
> On Tue, 2008-09-16 at 14:50 +0200, Xu Yang wrote:
> > Hi guys,
> >
> > I am looking for a function that can show me the current thread is
> > running on which cpu.
>
> > e.g I am using pthread to write a multithreaded program, in each
> > thread I would like to insert such kind of function so that I can know
> > on which cpu this thread is running on.
>
> That doesn't make much sense as the same thread can run on a different
> CPU after each scheduling decision. And - as it is in userspace -
> scheduling can happen before any assembler op.
>
>        Bernd
> --
> Firmix Software GmbH                   http://www.firmix.at/
> mobil: +43 664 4416156                 fax: +43 1 7890849-55
>          Embedded Linux Development and Services
>
>
>

Re: looking for a function

[Arjan van de Ven]

On Tue, 16 Sep 2008 16:11:10 +0200
"Xu Yang" <risingsunxy@googlemail.com> wrote:

> Hi Bernd,
> 
> thanks for you reply.
> 
> yes, I know the thread migrates all the time, this is exactly what I
> would like to observe. I would like to learn about the thread
> migration of some specific scheduling algorithm. so ....
> 
> any idea about the function?

the getcpu() system call will do what you want.



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org

Re: looking for a function

[Xu Yang]

Hi Arjan,

thanks,
I will try that!

Best regards,

Yang

2008/9/16, Arjan van de Ven <arjan@infradead.org>:
> On Tue, 16 Sep 2008 16:11:10 +0200
> "Xu Yang" <risingsunxy@googlemail.com> wrote:
>
> > Hi Bernd,
> >
> > thanks for you reply.
> >
> > yes, I know the thread migrates all the time, this is exactly what I
> > would like to observe. I would like to learn about the thread
> > migration of some specific scheduling algorithm. so ....
> >
> > any idea about the function?
>
> the getcpu() system call will do what you want.
>
>
>
> --
> Arjan van de Ven        Intel Open Source Technology Centre
> For development, discussion and tips for power savings,
> visit http://www.lesswatts.org
>

Re: looking for a function

[Frédéric Weisbecker]

2008/9/16 Xu Yang <risingsunxy@googlemail.com>:
> Hi Bernd,
>
> thanks for you reply.
>
> yes, I know the thread migrates all the time, this is exactly what I
> would like to observe. I would like to learn about the thread
> migration of some specific scheduling algorithm. so ....
>
> any idea about the function?
>

And perhaps you should have a look at the sched_switch tracer which
will log for you the different context switches.

Regards,

Frederic.

Re: looking for a function

[Xu Yang]

Hi Frederic,

thank you very much!
this is very useful for me. :-)

Best regards,

Yang

2008/9/16, Frédéric Weisbecker <fweisbec@gmail.com>:
> 2008/9/16 Xu Yang <risingsunxy@googlemail.com>:
> > Hi Bernd,
> >
> > thanks for you reply.
> >
> > yes, I know the thread migrates all the time, this is exactly what I
> > would like to observe. I would like to learn about the thread
> > migration of some specific scheduling algorithm. so ....
> >
> > any idea about the function?
> >
>
> And perhaps you should have a look at the sched_switch tracer which
> will log for you the different context switches.
>
> Regards,
>
> Frederic.
>

Re: looking for a function

[Chris Snook]

Xu Yang wrote:
> Hi Bernd,
> 
> thanks for you reply.
> 
> yes, I know the thread migrates all the time, this is exactly what I
> would like to observe. I would like to learn about the thread
> migration of some specific scheduling algorithm. so ....
> 
> any idea about the function?
> 
> Best regards,
> 
> Yang

getcpu() should do what you want.

-- Chris

> 2008/9/16, Bernd Petrovitsch <bernd@firmix.at>:
>> Hi!
>>
>> On Tue, 2008-09-16 at 14:50 +0200, Xu Yang wrote:
>>> Hi guys,
>>>
>>> I am looking for a function that can show me the current thread is
>>> running on which cpu.
>>> e.g I am using pthread to write a multithreaded program, in each
>>> thread I would like to insert such kind of function so that I can know
>>> on which cpu this thread is running on.
>> That doesn't make much sense as the same thread can run on a different
>> CPU after each scheduling decision. And - as it is in userspace -
>> scheduling can happen before any assembler op.
>>
>>        Bernd
>> --
>> Firmix Software GmbH                   http://www.firmix.at/
>> mobil: +43 664 4416156                 fax: +43 1 7890849-55
>>          Embedded Linux Development and Services
>>
>>
>>
> --
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> Please read the FAQ at  http://www.tux.org/lkml/

looking for a function

[Xu Yang]

Hi guys,

I am looking for a function that can show me the current thread is
running on which cpu.

e.g I am using pthread to write a multithreaded program, in each
thread I would like to insert such kind of function so that I can know
on which cpu this thread is running on.

which function should be used?

thanks for the help!!

best regards,



Yang

Re: looking for a function

[Steve Graegert]

Xu Yang,

On Linux sched_getcpu(3) comes to mind.  This function is not
particularly useful since the information returned by the function
might not be correct at the point of its return as threads can be
switched to other CPUs (read: cores) at anytime (although CPU/core
switching can be quite expensive due to cache line bouncing for
instance)

So, once the information has been obtained it might already be
obsolete.  Anyway, I hope that is what you're looking for.

        \Steve

--

Steve Grägert


On Tue, Sep 16, 2008 at 3:26 PM, Xu Yang <risingsunxy@googlemail.com> wrote:
>
> Hi guys,
>
> I am looking for a function that can show me the current thread is
> running on which cpu.
>
> e.g I am using pthread to write a multithreaded program, in each
> thread I would like to insert such kind of function so that I can know
> on which cpu this thread is running on.
>
> which function should be used?
>
> thanks for the help!!
>
> best regards,
>
>
>
> Yang
> --
> To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
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To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
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Re: looking for a function

[Xu Yang]

Hi Steve,

thanks for your reply :-)

I will try this. I am evaluating some scheduling algorithm, so I would
like to learn about how the threads migrate. That is why I am asking
for such kind of function.

thank for your help!

Bes regards,

Yang

2008/9/16, Steve Graegert <graegerts@gmail.com>:
> Xu Yang,
>
> On Linux sched_getcpu(3) comes to mind.  This function is not particularly
> useful since the information returned by the function might not be correct
> at the point of its return as threads can be switched to other CPUs (read:
> cores) at anytime (although CPU/core switching can be quite expensive due to
> cache line bouncing for instance)
>
> So, once the information has been obtained it might already be obsolete.
> Anyway, I hope that is what you're looking for.
>
>         \Steve
>
> --
>
> Steve Grägert
>
>
>
> On Tue, Sep 16, 2008 at 3:26 PM, Xu Yang <risingsunxy@googlemail.com> wrote:
> >
> > Hi guys,
> >
> > I am looking for a function that can show me the current thread is
> > running on which cpu.
> >
> > e.g I am using pthread to write a multithreaded program, in each
> > thread I would like to insert such kind of function so that I can know
> > on which cpu this thread is running on.
> >
> > which function should be used?
> >
> > thanks for the help!!
> >
> > best regards,
> >
> >
> >
> > Yang
> > --
> > To unsubscribe from this list: send the line "unsubscribe
> linux-c-programming" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at
> http://vger.kernel.org/majordomo-info.html
> >
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

looking for a function

[Xu Yang]

Hi guys,

I am looking for a function that can show me the current thread is
running on which cpu.

e.g I am using pthread to write a multithreaded program, in each
thread I would like to insert such kind of function so that I can know
on which cpu this thread is running on.

which function should be used?

thanks for the help!!

best regards,



Yang

looking for a function

[Xu Yang]

Hi guys,

I am looking for a function that can show me the current thread is
running on which cpu.

e.g I am using pthread to write a multithreaded program, in each
thread I would like to insert such kind of function so that I can know
on which cpu this thread is running on.

which function should be used?

thanks for the help!!

best regards,


Yang