pthread_use_only_cpu(3)pthread_use_only_cpu(3)NAMEpthread_use_only_cpu - Restricts a thread to running only on the speci‐
fied CPU. If that CPU is unavailable for any reason, the thread will
#include <cpuset.h> #include <sys/types.h>
long flag );
DECthreads POSIX 1003.1c Library (libpthread.so)
Thread to be restricted to use only the specified CPU. Currently only
PTHREAD_BINDCPU_INFLEXIBLE is defined, and must be specified.
This routine restricts thread to cpu_id, preventing the thread from
utilizing any other available processor resources even when cpu_id may
be busy for an extended time with other work or is otherwise unavail‐
This function can be used only with System Contention Scope (SCS)
threads, that is, threads that were created using an attributes object
with the scope attribute set to PTHREAD_SCOPE_SYSTEM.
Specifying a cpu_id value of CPU_NONE removes the restriction from the
thread, allowing it to again take advantage of any available CPU when
the CPU on which it last ran is busy.
cpu_id will become unavailable if the corresponding CPU is removed from
the processor set in which the process is running or if it is taken
off-line. In this event, any thread that is restricted to cpu_id will
not run until pthread_use_only_cpu is called from another thread to
change or remove the thread's restriction.
Threads that have not been restricted to a specific CPU using this
function are typically scheduled to run on the CPU they last used, in
order to take advantage of valid cache and translation buffer (TB)
entries. However, if that CPU remains busy with other work, the threads
may instead be run on another CPU if available. This default behavior
is the most effective except in extremely unusual circumstances, so
this function should be used only with great caution. Improper use of
this function can substantially degrade application performance; proper
use will rarely improve performance measurably (if at all).
This routine does not prevent cpu_id from performing other work.
Restricting a thread to a CPU is rarely beneficial to an application
since other threads of equal or higher priority may be run by cpu_id,
and, in addition to preventing thread from executing, this activity
will likely invalidate cache and TB entries used by thread, thereby
removing the principal advantages of having restricted the thread. Fur‐
thermore, giving a thread a very high priority is not sufficient to
guarantee exclusive use of a CPU since page faults, interrupts, or
blocking system calls of even very short duration can permit other
threads to obtain the CPU. To obtain exclusive use of a CPU, see the
processor_sets(4) reference page.
If an error condition occurs, the target thread's scheduling restric‐
tions remain unchanged, and this routine returns an integer value indi‐
cating the type of error. Possible return values are as follows: Suc‐
cessful completion. The value specified by cpu_id is invalid, or the
flag is invalid. The specified thread is a Process Contention Scope
thread. The specified thread does not exist.
Functions: pthread_create(3), pthread_attr_init(3),
Manuals: Guide to DECthreads and Programmer's Guide