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Date: Fri, 4 Feb 2011 15:05:45 -0500
Message-ID: <AANLkTimZTbWt19hg8XWxL+Q5TBFY0P8wF-TfFDLYjBCw@mail.gmail.com>
Subject: Re: Thread Affinity structure
From: Sri Ram Vemulpali <sri.ram.gmu06@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: Kernel-newbies <kernelnewbies@nl.linux.org>,
        linux-kernel-mail <linux-kernel@vger.kernel.org>
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Hi Christoph,

  Thanks for response. Can you please explain in little bit elaborate
what do you mean

 "The value returned ?from a call to gettid(2) can be passed in the argument
 pid. ?Specifying pid as 0 will set the attribute for the calling thread,
 and passing the value returned from a call to getpid(2) will set the
 attribute for the main thread of the thread group."

To whom I should pass the id. I did not understood.

Thanks,
Sri.

On Fri, Feb 4, 2011 at 2:29 PM, Christoph Lameter <cl@linux.com> wrote:
> On Fri, 4 Feb 2011, Sri Ram Vemulpali wrote:
>
>> ? ? I have doubt regarding how the thread affinity (to processor) is
>> defined in a process (task). If there is only single thread in a
>> process, then when process calls itself on binding to a core, will let
>> run on that core forever. But, what if there are multiple threads, in
>> a process (task). If the main thread calls set affinity to a core, is
>> it going to get inherited to all other threads, or just the calling
>> thread in a task. What happens when forked a process with threads that
>> has affinity to a core. Please can anyone point me to the literature
>> on this. Thanks in advance.
>
> See "man sched_setaffinity"
>
> "
> The affinity mask is actually a per-thread attribute that can be
> adjusted independently for each of the threads in a thread group. ?The
> value returned ?from a call to gettid(2) can be passed in the argument
> pid. ?Specifying pid as 0 will set the attribute for the calling thread,
> and passing the value returned from a call to getpid(2) will set the
> attribute for the main thread of the thread group. ?(If you ?are ?using
> the ?POSIX threads API, then use pthread_setaffinity_np(3) instead of
> sched_setaffinity().)
> "
>
>
>
> The setting of the affinity occurs for the running thread if pid == 0.
> Affinity masks are inherited across forks.
>
>
>
>
>
>


-- 
Regards,
Sri.
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