Re: Thread Affinity structure

[Christoph Lameter]

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.





--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/