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SubjectRe: Thread Affinity structure
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.







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