06-09-2002
actual cause of slowness?
Do we really know if the slowness observed is caused by resource contention (many process contenting one SHMEM) or is caused by resource utilisation (the path length of the code doing the SHMEN access)?
If the actual cause is contention, and the process es appeared slow because they spend most of their time waiting, one of the solutions is to have more resouces (multiple SHEM? and pack them up by tge background process).
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LEARN ABOUT CENTOS
pthread_attr_getscope
PTHREAD_ATTR_SETSCOPE(3) Linux Programmer's Manual PTHREAD_ATTR_SETSCOPE(3)
NAME
pthread_attr_setscope, pthread_attr_getscope - set/get contention scope attribute in thread attributes object
SYNOPSIS
#include <pthread.h>
int pthread_attr_setscope(pthread_attr_t *attr, int scope);
int pthread_attr_getscope(pthread_attr_t *attr, int *scope);
Compile and link with -pthread.
DESCRIPTION
The pthread_attr_setscope() function sets the contention scope attribute of the thread attributes object referred to by attr to the value
specified in scope. The contention scope attribute defines the set of threads against which a thread competes for resources such as the
CPU. POSIX.1-2001 specifies two possible values for scope:
PTHREAD_SCOPE_SYSTEM
The thread competes for resources with all other threads in all processes on the system that are in the same scheduling allocation
domain (a group of one or more processors). PTHREAD_SCOPE_SYSTEM threads are scheduled relative to one another according to their
scheduling policy and priority.
PTHREAD_SCOPE_PROCESS
The thread competes for resources with all other threads in the same process that were also created with the PTHREAD_SCOPE_PROCESS
contention scope. PTHREAD_SCOPE_PROCESS threads are scheduled relative to other threads in the process according to their schedul-
ing policy and priority. POSIX.1-2001 leaves it unspecified how these threads contend with other threads in other process on the
system or with other threads in the same process that were created with the PTHREAD_SCOPE_SYSTEM contention scope.
POSIX.1-2001 requires that an implementation support at least one of these contention scopes. Linux supports PTHREAD_SCOPE_SYSTEM, but not
PTHREAD_SCOPE_PROCESS.
On systems that support multiple contention scopes, then, in order for the parameter setting made by pthread_attr_setscope() to have effect
when calling pthread_create(3), the caller must use pthread_attr_setinheritsched(3) to set the inherit-scheduler attribute of the
attributes object attr to PTHREAD_EXPLICIT_SCHED.
The pthread_attr_getscope() function returns the contention scope attribute of the thread attributes object referred to by attr in the buf-
fer pointed to by scope.
RETURN VALUE
On success, these functions return 0; on error, they return a nonzero error number.
ERRORS
pthread_attr_setscope() can fail with the following errors:
EINVAL An invalid value was specified in scope.
ENOTSUP
scope specified the value PTHREAD_SCOPE_PROCESS, which is not supported on Linux.
CONFORMING TO
POSIX.1-2001.
NOTES
The PTHREAD_SCOPE_SYSTEM contention scope typically indicates that a user-space thread is bound directly to a single kernel-scheduling
entity. This is the case on Linux for the obsolete LinuxThreads implementation and the modern NPTL implementation, which are both 1:1
threading implementations.
POSIX.1-2001 specifies that the default contention scope is implementation-defined.
SEE ALSO
pthread_attr_init(3), pthread_attr_setaffinity_np(3), pthread_attr_setinheritsched(3), pthread_attr_setschedparam(3),
pthread_attr_setschedpolicy(3), pthread_create(3), pthreads(7)
COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2013-04-19 PTHREAD_ATTR_SETSCOPE(3)