Setting of Priorities

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SETTING OF PRIORITIES

IN SYSTEMS MANAGEMENT

How to set Priorities

Being able to set priorities is the key to getting organized and making the most of your time .

But how do you set priorities for your day-to-day tasks and activities as well as specific action items for your goals in order to make sure youre not letting anything slip through the cracks?

You will have daily priorities such as taking the kids to school, and you should also have daily goalspecific actions these all need to be prioritized into one seamless set of action items to make sure your day-to-day life doesnt take precedence over your goals and vice versa.

To prioritize day-to-day activities and goal specific Action Items, try any one of the following systems:

Must Do | Should Do | Nice to do

Priority 1: Must Do these goals or activities must be achieved if you are to consider yourself successful. These are your highest priority goals or activities.

Priority 2: Should Do these goals or activities should be achieved (but it is not essential) toconsider yourself successful.

Priority 3: Nice to Do self explanatory.

You may prefer the commonly used High | Medium | Low priority terminology.

Ranking system - where you number all tasks in the order that you need to do them, from 1 being mostimportant (do this one first) to however many action items there are on your list.

Urgent | Important activity matrix Another popular way of prioritizing action items is the Urgent | Importantactivity matrix originally developed by time and organizational management guru Stephen Covey .

This matrix is based on all tasks being assigned a level of urgency and importance as illustrated below .
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Urgent-Important Matrix for setting priorities

Human nature means that we instinctively act on tasks that are urgent, whether these tasks areimportant or not. Thats OK for the tasks that are also important, but the other ones are not necessarilythe best use of your time and effort.

This matrix can also be used to explain why taking action on goals sometimes gets into trouble. Goals aretypically derived from dreams and desires, which by their very nature are not urgent. Goals are however VERY important and their enabling actions need to be elevated in priority over tasks that are not reallyimportant.

So as a tool for helping you prioritize your action items, start by identifying which part of the matrix eachtask belongs in, and then manage them as follows:


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Urgent- Important Matrix for setting priorities

Most importantly, find that suits you set priorities prioritizing tasks is the key to time management andorganization and is essential if you have any hope of achieving your goals. And don't forget to documentyour set priorities in your action plan.

Find out more on setting priorities from the expert - Stephen Covey!
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Setting Priorities

When you have to choose among several tasks, there are several prioritization tools you can use. Keyones are summarized below. If you are in a rut with your prioritization method, experimenting with thefollowing methods may yield the one that is right for you.

Note that it is commonly recognized that 20% of your activities will account for 80 percent of your success (The Pareto Principle). Hence, if you have 100 tasks in your task list, probably about 20 of thosewill be the key ones to focus on. Hence, whatever prioritization method you use, you should ensure ithelps you pinpoint these tasks.

Covey's Quadrants

Stephen Covey describes a high-level prioritization scheme in his book The Seven Habits of Highly Effective People . In this scheme, tasks are categorized by four quadrants:

QI - Important and Urgent QII - Important but Not Urgent

QIII - Not Important but Urgent QIV - Not Important and Not Urgent

Dr. Covey notes that highly effective people make time for the QII activities , and that doing so canreduce the time spent in other quadrants. While QI - QIV prioritization doesn't help you decide which QIactivity to do first and which to do second, and so on, it can be very enlightening to find out whichquadrants your tasks are in.

The ABC Method

I first became aware of this scheme when I used a paper-based Franklin planner.

It ranks tasks into three categories:

A = vital B = important C = nice

Then it subdivides tasks in these categories into A1, A2, A3... B1, B2 ... and so forth. Note that the A, B, Ccategories have a straight forward correspondence to Quadrants I, II, and III discussed in Covey's The 7 Habits of Highly Effective People . A lot of people find this prioritization method to be very helpful.Although the standard Pocket PC and Palm Task list application does not support these exact priorities,there are some very good third party applications that do. For example, Pocket Informant and AgendaFusion for the Pocket PC support prioritization and add a number of other useful capabilities.

The Payoff versus Time Method

With this method, you weight each task by the payoff you expect from it versus the time it takes todo it . Tasks that have high payoff and that take little time are the ones you would do first.Correspondingly, tasks that have low payoff and that take a lot of time are ones you would do last or notat all.
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Closing Thoughts

Sometimes priorities shift. We've all had to juggle tasks. On balance, though, we need to ensure our priorities are consistent with our personal goals and the goals of our organizations. Doing this requires aperiodic review, and a weekly planning session is ideal for this.

Also, while the message has been out for years that organizations should clearly communicate their goalsand priorities, research continues to show that many organizations are not good at this. Hence, you mayneed to make an effort to identify the goals and priorities of your organization, to ensure your priorities areconsistent with those.

Finally, to emphasize what was pointed out earlier, you should take full advantage of the Pareto Principle.The best discussion I have ever seen of this is in Tim Ferriss' book The 4-Hour Workweek: Escape 9-5, Live Anywhere, and Join the New Rich . While the title of this book makes it sound like one of the millionsof get-rich-quick hypes, this is truly a phenomenal book about lifestyle design with some great discussionsof managing time and setting priorities. Amazon is practically giving it away at its $12 price. I ampersonally convinced that Ferriss is the New Time Management Guru.
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Setting your Priorities

To harness this extra performance and integration while taming the complexity of modern applications the use of a real time operating system (RTOS) is becoming more commonplace. A key feature of anRTOS is that of multitasking. A multitasking environment allows a program to be broken down intomultiple tasks with each one 'thinking' it has the cpu to itself. It is like having multiple cpus.

A modern RTOS will use priority based scheduling of tasks and this article will discuss how scheduling isundertaken. One aspect of scheduling in a priority based system is the allocation of priorities to the

various tasks. Often, what is deemed the most important task will be given the highest priority, but thisisn't necessarily the most efficient method of priority allocation. Schemes for assigning priorities anddetermining whether a system can meet its scheduling deadlines will also be discussed.

RTOS scheduling

The scheduler is the part of the RTOS that decides which task should be running on the cpu at any giventime. In normal execution, a task performs the functionality of the user's application and will then make ablocking call of some sort; for example, an OS derived time delay or waiting for a semaphore or other signal from an interrupt service routine (ISR) or another task. A blocked task will be suspended by theoperating system and another task run. When the time delay expires or the event occurs, the taskunblocks and can be scheduled to run by the OS. If a low priority task is running on the cpu and a high

priority task becomes ready to run in a pre emptive priority based system, a context switch will occur thelow priority task will suspended and the high priority task will be given the cpu. The low priority task is saidto be pre empted by the high priority task.

Assigning task priorities

The majority of RTOSs implement pre emptive priority based scheduling as this is well suited toembedded systems requiring fast response to real time events. But how does the engineer actuallyassign priorities to tasks in the system? Giving the most important task in the system the highest prioritymay not have the desired effect.

There are a number of methods of assigning priorities, including: Earliest Deadline First; Deadline-Monotonic Scheduling; and Rate-Monotonic Scheduling.

Earliest Deadline First (EDF) scheduling uses a queue of tasks in order of priority. When a task blocks,the RTOS searches the queue for the task closest to its deadline and selects it as the next to run. This isa useful scheme as it is possible to guarantee all task deadlines are met at high levels of cpu utilization.However, there is a cost in terms of complexity and execution time of the RTOS scheduler code.

Deadline-Monotonic Scheduling is a fixed priority pre emptive priority allocation scheme wherepriorities are assigned by giving the task with shortest deadline the highest priority. This assignmentscheme is suited to tasks which have deadlines equal to or less than their periods and have worst case


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execution times equal to or less than their deadlines.

Rate-Monotonic Scheduling (RMS) , meanwhile, is a fixed priority pre emptive priority allocation schemegaining in popularity. Being a fixed priority scheme, no special modification to the RTOS is necessary.With RMS, it is possible to guarantee that a key set of tasks will meet their deadlines and that the systemis schedulable. A further benefit is that system performance degrades gracefully during overloadconditions, with the lowest priority tasks missing deadlines.

RMS assumes:* All tasks are periodic* All tasks have deterministic deadlines equal to their periods* Tasks do not share resources; for example, no blocking semaphores* Tasks have fixed priorities and the highest priority task will always run* Tasks with shortest deadlines (periods) have the highest priorities* Context switches and RTOS operations use no cpu resources

The key point here is that the highest priority is allocated to the task with the shortest period. The nexthighest priority is assigned to the task with the next shortest period and so on. Using Rate-MonotonicAnalysis (RMA), it is possible to determine whether a system with task priorities allocated in this way canbe scheduled or, in other words, whether critical tasks will miss any deadlines.

Under RMA, the second point above is relaxed and tasks no longer need to have equal periods anddeadlines, so long as the deadline is less than or equal to the period. For example, a task may have aperiod (T) of 150ms and a computation time (C) of 50ms. This means the task must be able to run for 50ms every 150ms. This allows us to calculate the utilization (U) of the cpu using the following equation:

U = ? Ci/Ti

The total utilization of the CPU is the sum of all the individual task utilizations. There are utilization limitsdependent upon the number of tasks, n, in the system, as given by a second equation:

n(nv2 -1)

As n grows, the utilization limit tends towards logn2, so the cpu utilization limit for n tasks is 0.693, or 69.3%. Providing the cpu utilization is less than 69.3%, the system can meet all deadlines. The remaining30% can be utilized for other tasks without hard real-time deadlines.

Consider the following example of a three task system:Task A: period = 150ms, computation time = 20msTask B: period = 80ms, computation time = 30msTask C: period = 15ms, computation time = 2ms

The task utilizations will therefore be:Task A: 13.33% [(20/150) x 100%]Task B: 37.5% [(30/80) x 100%]Task C: 13.33% [(2/15) x 100%]

The total utilization becomes 64.16%. As long as the priorities are assigned in the ascending order TaskC > Task B > Task A, the system will be schedulable as the utilization value is less than 69.3%.It is possible to extend RMA further to take into account context switching time and to modify the systemwhen non periodic tasks are used and when shared resources are part of the system.


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Setting of Priorities

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