difference between contiguous and non contiguous memory allocation

                                                                              Operating System          

Processor Affinity

Processor Affinity means a process has an affinity for the processor on which it is currently running. When a process runs on a specific processor, there are certain effects on the cache memory. The data most recently accessed by the process populate the cache for the processor. As a result, successive memory access by the process is often satisfied in the cache memory.

Now, suppose the process migrates to another processor. In that case, the contents of the cache memory must be invalidated for the first processor, and the cache for the second processor must be repopulated. Because of the high cost of invalidating and repopulating caches, most SMP(symmetric multiprocessing) systems try to avoid migrating processes from one processor to another and keep a process running on the same processor. This is known as processor affinity. There are two types of processor affinity, such as:

1. Soft Affinity: When an operating system has a policy of keeping a process running on the same processor but not guaranteeing it will do so, this situation is called soft affinity.
2. Hard Affinity: Hard Affinity allows a process to specify a subset of processors on which it may run. Some Linux systems implement soft affinity and provide system calls like sched_setaffinity() that also support hard affinity.
   

   Load Balancing

   Load Balancing is the phenomenon that keeps the workload evenly distributed across all processors in an SMP system. Load balancing is necessary only on systems where each processor has its own private queue of a process that is eligible to execute.

   Load balancing is unnecessary because it immediately extracts a runnable process from the common run queue once a processor becomes idle. On SMP (symmetric multiprocessing), it is important to keep the workload balanced among all processors to utilize the benefits of having more than one processor fully. One or more processors will sit idle while other processors have high workloads along with lists of processors awaiting the CPU. There are two general approaches to load balancing:

   
   1. Push Migration: In push migration, a task routinely checks the load on each processor. If it finds an imbalance, it evenly distributes the load on each processor by moving the processes from overloaded to idle or less busy processors.
   2. Pull Migration:Pull Migration occurs when an idle processor pulls a waiting task from a busy processor for its execution.