we can apply the any algo on any level of queue. we can apply fifo, sjf(short job first) and round robin at any level. by doing this the efficiency of completing the process can be increased and every process will take the cpu burst
Windows XP uses a quantum-based, preemptive priority scheduling algorithm
The advantage of multilevel queue scheduling is that it covers all disadvantage of all others scheduling...................... The main disadvantage of multilevel queue scheduling is that it is very difficult to understand and it takes a lot of time........ By waqar ahmad awan (0333-9996376)
Multi-level scheduling method for multiplexing packets in a communications networkA method and system for data traffic management in telecommunications networks is presented. End user data streams are aggregated to achieve more efficient use of a communication channel. Bandwidth is dynamically allocated to the data streams of the various users, effectively reducing their communications costs. The system includes a class of service selector and a plurality of stream selectors. Each stream selector is associated with a single budget category. Data is placed into queues according to a priority assigned by the end user. Data packets are transmitted from their queues through the class of service selector and through one of the stream selectors in response to the traffic provided by the end users and the budget category subscriptions of the end users.
A variant of round robin scheduling is called selfish round robin scheduling. In selfish round robin, there is a maximum limit on the number of processes that can be placed in the round-robin queue (including the process being executed by the CPU). After that maximum is reached, newly entering processes are placed on a holding queue. Processes in the holding queue do not get any time slice of the CPU. When a process in the round-robin queue completes and leaves the system, the oldest process in the holding queue is allowed to enter the round-robin queue
The circular queue data structure is required to implement the round robin scheduling policy. Round robin is similar to FCFS scheduling.
By far the simplest CPU-scheduling algorithm is the first-come, first-served (FCFS) scheduling algorithm. With this scheme, the process that requests the CPU first is allocated the CPU first. The implementation of the FCFS policy is easily managed with a FIFO queue. When a process enters the ready queue, its PCB is linked onto the tail of the queue. When the CPU is free, it is allocated to the process at the head of the queue. The running process is then removed from the queue. The code for FCFS scheduling is simple to write and understand. The average waiting time under the FCFS policy, however, is often quite long. Consider the following set of processes that arrive at time 0, with the length of the CPU-burst time given in milliseconds:
After certain time if we increase the priority then lower priority jobs will get chance fast.this process is called aging.it is used for multilevel feedback queue.
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in roundrobin scheduling each process is gven a fixed time to execute so whenever a new process arrives it is placed at the end of the queue,,,,,the advantage by doing this type of scheduling is response time will be gud...But the disadvantage waiting time is more
the total time that staying in the queue that wait for process of each process.
Advantages of Multilevel Inverter:The multilevel converter has a several advantages, that is:1. Common Mode Voltage: The multilevel inverters produce common mode voltage, reducing the stress of the motor and don't damage the motor.2. Input Current: Multilevel inverters can draw input current with low distortion3. Switching Frequency: The multilevel inverter can operate at both fundamental switching frequencies that are higher switching frequency and lower switching frequency. It should be noted that the lower switching frequency means lower switching loss and higher efficiency is achieved.4. Reduced harmonic distortion: Selective harmonic elimination technique along with the multi level topology results the total harmonic distortion becomes low in the output waveform without using any filter circuit.
A multi-level feedback queue scheduling policy gives preference to short and I/O bound processes, it also rapidly establishes the nature of a process and schedules it accordingly. Multi-level feedback queues work on priorities. Processes are placed in separate queues based on their priority, this in turn is based on their CPU consumption and If a process uses too much of the CPU, it will be given a lower priority and therefore get less CPU time than fast and I/O bound processes. Any processes that do not complete in their allocated time slice / quantum are demoted to a queue of less priority, these lower priority queues generally have larger quantums / time slices. Each of the queues may use a different scheduling algorithm, this is done to make the overall scheduling method as efficient as possible. The features that may vary between different multi-level feedback queue scheduling methods are: - The number of queues - The scheduling algorithm assigned to each queue - The method used to promote/demote processes to different queues - The method that determines which queue a process enters --- Thomas Lee