IBM REDP-4285-00 User Manual
Chapter 1. Understanding the Linux operating system
5
Draft Document for Review May 4, 2007 11:35 am
4285ch01.fm
From the performance perspective, thread creation is less expensive than process creation
because a thread does not need to copy resources on creation. On the other hand, processes
and threads have similar characteristics in term of scheduling algorithm. The kernel deals
with both of them in the similar manner.
because a thread does not need to copy resources on creation. On the other hand, processes
and threads have similar characteristics in term of scheduling algorithm. The kernel deals
with both of them in the similar manner.
Figure 1-4 process and thread
In current Linux implementations, a thread is supported with the POSIX (Portable Operating
System Interface for UNIX) compliant library (
System Interface for UNIX) compliant library (
pthread
). There are several thread
implementations available in the Linux operating system. The following are the widely used.
LinuxThreads
LinuxThreads have been the default thread implementation since Linux kernel 2.0 was
available. The LinuxThread has some noncompliant implementations with the POSIX
standard. NPTL is taking the place of LinuxThreads. The LinuxThreads will not be
supported in future release of Enterprise Linux distributions.
available. The LinuxThread has some noncompliant implementations with the POSIX
standard. NPTL is taking the place of LinuxThreads. The LinuxThreads will not be
supported in future release of Enterprise Linux distributions.
Native POSIX Thread Library (NPTL)
The NPTL was originally developed by Red Hat. NPTL is more compliant with POSIX
standards. Taking advantage of enhancements in kernel 2.6 such as the new clone()
system call, signal handling implementation etc., it has better performance and scalability
than LinuxThreads.
standards. Taking advantage of enhancements in kernel 2.6 such as the new clone()
system call, signal handling implementation etc., it has better performance and scalability
than LinuxThreads.
There is some incompatibility with LinuxThreads. An application which has a dependence
on LinuxThread may not work with the NPTL implementation.
on LinuxThread may not work with the NPTL implementation.
Next Generation POSIX Thread (NGPT)
NGPT is an IBM developed version of POSIX thread library. It is currently under
maintenance operation and no further development is planned.
maintenance operation and no further development is planned.
Using the LD_ASSUME_KERNEL environment variable, you can choose which threads library the
application should use.
application should use.
1.1.4 Process priority and nice level
Process priority
is a number that determines the order in which the process is handled by the
CPU and is determined by dynamic priority and static priority. A process which has higher
process priority has higher chances of getting permission to run on processor.
process priority has higher chances of getting permission to run on processor.
The kernel dynamically adjusts dynamic priority up and down as needed using a heuristic
algorithm based on process behaviors and characteristics. A user process can change the
static priority indirectly through the use of the
algorithm based on process behaviors and characteristics. A user process can change the
static priority indirectly through the use of the
nice
level of the process. A process which has
higher static priority will have longer time slice (how long the process can run on processor).
Process
Process
resource
e
resource
resourc
resource
resource
e
resource
resource
copy
Process
Thread
Thread
Threa
ad
Thread
Thread
Thread
Threa
ad
Thread
resource
e
resource
resource
share
share
Process creation
Thread creation