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 22.3 Process CPU Priority And Scheduling
 ========================================
 
 When multiple processes simultaneously require CPU time, the system's
 scheduling policy and process CPU priorities determine which processes
 get it.  This section describes how that determination is made and GNU
 C library functions to control it.
 
    It is common to refer to CPU scheduling simply as scheduling and a
 process' CPU priority simply as the process' priority, with the CPU
 resource being implied.  Bear in mind, though, that CPU time is not the
 only resource a process uses or that processes contend for.  In some
 cases, it is not even particularly important.  Giving a process a high
 "priority" may have very little effect on how fast a process runs with
 respect to other processes.  The priorities discussed in this section
 apply only to CPU time.
 
    CPU scheduling is a complex issue and different systems do it in
 wildly different ways.  New ideas continually develop and find their
 way into the intricacies of the various systems' scheduling algorithms.
 This section discusses the general concepts, some specifics of systems
 that commonly use the GNU C library, and some standards.
 
    For simplicity, we talk about CPU contention as if there is only one
 CPU in the system.  But all the same principles apply when a processor
 has multiple CPUs, and knowing that the number of processes that can
 run at any one time is equal to the number of CPUs, you can easily
 extrapolate the information.
 
    The functions described in this section are all defined by the
 POSIX.1 and POSIX.1b standards (the `sched...' functions are POSIX.1b).
 However, POSIX does not define any semantics for the values that these
 functions get and set.  In this chapter, the semantics are based on the
 Linux kernel's implementation of the POSIX standard.  As you will see,
 the Linux implementation is quite the inverse of what the authors of the
 POSIX syntax had in mind.

Menu

 
* Absolute Priority               The first tier of priority.  Posix
* Realtime Scheduling             Scheduling among the process nobility
* Basic Scheduling Functions      Get/set scheduling policy, priority
* Traditional Scheduling          Scheduling among the vulgar masses
* CPU Affinity                    Limiting execution to certain CPUs
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