Hi all,
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.
--
Regards,
Sri.
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.
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 <[email protected]> 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.
On Fri, 4 Feb 2011, Sri Ram Vemulpali wrote:
> 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.
The passage was from the man page that you get by typing
man sched_setaffinity
You pass the id as a parameter to sched_setaffinity.