CHAPTER OVERVIEW

This chapter is dedicated to the correct and reliable communication of values in shared-memory multiprocessors. Relevant correctness properties of the memory system of shared-memory multiprocessors include coherence, the memory consistency model (henceforth also referred to as the memory model), and the reliable execution of synchronization primitives. Since chip multiprocessors are designed as shared-memory multi-core systems, this chapter targets correctness issues not only in symmetric multiprocessors (SMPs) or large-scale cache coherent distributed shared-memory systems (cc-NUMAs and COMAs) covered in Chapter 5, but also in chip multiprocessors with core multi-threading (CMPs) covered in Chapter 8.

The correctness of a shared-memory multi-threaded program must be independent of the relative execution speed of its threads, because of the numerous unpredictable events that can disrupt the execution of any one thread, such as DVFS (dynamic voltage and frequency scaling), thermal emergencies, conflicts for hardware and software resources, interrupts, exceptions, kernel activity, thread scheduling, data allocation delays, and interactions with other running programs. If a multi-threaded program is written for a dedicated machine in which timing is highly predictable and the program is written in a way that takes timing into account for its correctness (such as, possibly, in real-time systems), many conclusions of this chapter should be revised. In other words, the target software throughout this chapter is portable shared-memory multi-threaded programs written for general-purpose or multi-purpose machines and includes the operating system kernel.

CHAPTER OVERVIEW

In this chapter we sharpen our focus on thread-level parallelism within a single die. Parallelism within a die comes in different forms. Within a single-core, multiple threads can be executed to improve resource utilization, an approach called core multi-threading. There are three approaches to core multi-threading depending on how and when instructions are fetched from multiple ready threads: block multi-threading, interleaved multi-threading and simultaneous multi-threading. We show the hardware additions and modifications necessary for each of these three multi-threading approaches to work within the contexts of traditional (single-threaded) in-order and out-of-order processors. We use example-driven approaches to show the performance advantages of finer-grain multi-threading over coarse-grain multithreading. The performance advantages come at additional hardware cost.

The next paradigm to provide on-die parallelism is exploiting multiple cores on the same chip. Chip multiprocessors (CMPs) are fast becoming ubiquitous in all walks of computing, from cell phones to datacenter servers. We explain the fundamental advantages of CMPs over traditional shared-memory multiprocessors (SMPs) mostly borne from the fact that all cores are tightly integrated on a single die by on-die interconnects.We describe three on-die interconnect topologies common today for building CMPs. When all cores on a CMP are identical, the CMP is said to be homogeneous. The cores in heterogeneous CMPs differ in their capabilities. We describe various heterogeneous CMP designs and the gamut of different performance and functionality possible.

1. ‘One must look with the heart’

2. ‘The men where you live,’ said the little prince, ‘raise five thousand roses in the same garden – and they do not find in it what they are looking for.’

3. ‘They do not find it,’ I replied.

4. ‘And yet what they are looking for could be found in a single rose, or in a little water.’

5. ‘Yes, that is true,’ I said.

6. And the little prince added: ‘But the eyes are blind. One must look with the heart.’

7. Antoine de Saint-Exupéry, The Little Prince

Introduction

Parents have long known, and it appears that child development researchers are growing more aware, that from birth to two years of age the child enjoys a rich and increasingly complex emotional and social experience of the world. Historically, researchers’ understanding of the parent–infant socioemotional relationship has undergone considerable transformation in the last century. The major changes that have taken place are:

• a greater understanding of the extent of the infant’s socioemotional capabilities

• the view of the infant as an active participant in the development of their capabilities

• a greater appreciation of the individual differences between infants.

1. ‘I never ask advice about growing’

2. ‘Seven years and six months!’ Humpty Dumpty repeated thoughtfully.

3. ‘An uncomfortable sort of age. Now if you’d asked my advice, I’d have said “Leave off at seven” – but it’s too late now.’

4. ‘I never ask advice about growing,’ Alice said indignantly.

5. ‘Too proud?’ the other inquired.

6. Alice felt even more indignant at this suggestion.

7. ‘I mean,’ she said ‘that one can’t help growing older.’

8. ‘One can’t perhaps,’ said Humpty Dumpty, ‘but two can. With proper assistance, you might have left off at seven.’

9. Lewis Carroll, Through the Looking Glass

Introduction

In this chapter consideration will be given to understanding the concept of ‘development’, reasons for studying child development, basic concepts underpinning such study, and the conduct of research. Finally, the reader will be introduced to some basic statistical terms. The nature of the family in Australia is discussed in the family life-cycle: 2.

Child development concepts

Since the beginning of this century, significant advances have been made in the study of children in terms of understanding the nature of development (e.g. Sroufe 2009). Overton (1998) has identified that one feature of development about which there is general universal understanding is that development implies ‘change’. Rather simplistically this notion has focused psychologists’ attention on ‘changes in observed behaviour across age’ (Overton 1998 , p. 109).

Introduction

From previous chapters we have seen that rapid advancements in gross and fine motor kills allow toddlers to enjoy a sense of physical independence from their care-givers. Similarly, the development of thinking skills allows toddlers to experiment with their environment and to learn to interact with it. All this takes place within the larger domain of family life as the care-givers learn to adjust to having a child in their midst. In the still larger domain of the culture within which the family lives, the young child is learning to interact with the broader community.

In addition to these physical and cognitive changes, toddlers develop significantly in their social and emotional relationships. An emerging sense of self or ‘me’ is reflected in a growing awareness of separateness from others. During toddlerhood, children learn to recognise when significant others are pleased or displeased with their behaviour. As children become more aware of the larger world and their place in it, their emotional responsiveness to the world increases in subtlety and sophistication.

CHAPTER OVERVIEW

Given the widening gaps between processor speed, main memory (DRAM) speed, and secondary memory (disk) speed, it has become more and more difficult in recent years to feed data and instructions at the speed required by the processor while providing the ever-expanding memory space expected by modern applications. Modern systems rely on a memory hierarchy based on speed, size, and cost, as illustrated in Figure 4.1. Left of the dotted line is the cache hierarchy. Right of the dotted line is the virtual memory hierarchy, which may include a disk cache (not shown).

It has been observed over the years that the speed gap between the processor (clocked at multiple gigahertz and executing multiple instructions per clock) and main memory (with access times in the tens or even hundreds of nanoseconds) is growing exponentially. This problem is commonly referred to as the memory wall. A hierarchy of multiple levels of caches with various sizes and access times are employed to bridge the speed gap. Moreover, caches at every level are becoming more and more complex to help reduce or hide the latency of cache misses. To support OoO dynamically scheduled processors, which may have more than ten memory accesses pending at any time, modern, lockup-free (non-blocking) caches are capable of handling multiple cache hits and misses at a time. Furthermore, data and instructions are prefetched in caches before they are needed. In this chapter we describe these enhancements to cache designs.

Introduction

In The Little Prince Antoine de Saint-Exupéry reminds us that there are other ways of looking at and understanding the world apart from through adult eyes. During the primary school years children make significant strides in terms of their cognitive development. This chapter describes the nature of some of the changes that occur in the way children think about and understand their world in middle childhood. Consideration is given to learning and the matter of motivation. The family life-cycle: 16 examines the matter of counselling children in families.

1. Angels whispering

2. Because I feel that, in the heavens above

3. The angels, whispering to one another,

4. Can find, among their burning terms of love,

5. None so devoted as that of ‘mother’,

6. Therefore by that dear name I long have called you.

7. Edgar Allan Poe, ‘To My Mother’

Introduction

From conception to birth a wondrous journey is undertaken. In the last weeks before birth the foetus is fully developed: the baby is about 48 centimetres in length and weighs about 2500 grams. Before birth they will grow up to another 3 centimetres and gain up to 800 grams. This extra weight will help protect the baby upon emerging from the cocooned environment of the womb to the outside world. In the womb the baby drinks up to 3 litres of amniotic fluid per day, thereby preparing to develop the stomach, kidneys and bladder. The amniotic fluid is excreted and the baby’s urine (free of toxins) supplies part of the new amniotic fluid. The baby has been practising breathing before birth, may develop hiccups at times and can suck their thumb. All the senses are developed and the baby can hear, taste, feel, smell and see. A few weeks before birth the baby moves into a head-down position in the pelvis. The baby is now ready to set out on the next stage of their journey through life.

In this chapter the focus will be on conception, embryonic development, birth and postnatal development. Children’s concept of family is discussed in the family lifecycle: 5.

1. ‘… still within the little children’s eyes’

2. I sought no more that after which I strayed

3. In face of man or maid;

4. But still within the little children’s eyes

5. Seems something, something that replies,

6. They at least are for me, surely for me!

7. I turned me to them very wistfully

8. But just as their young eyes grew sudden fair

9. With dawning answers there

10. Their angel plucked them from me by the hair.

11. Francis Thompson, ‘The Hound of Heaven’

Introduction

General and academic interest in the study of child development has continued to increase. The interest in the field extends broadly across various disciplines. For example, a report in April 2009 by the US-based Robert Wood Johnson Foundation concluded that interventions most likely to improve the health of all Americans were ‘programs that promote early childhood development and that support children and families’. A report from Brazil recommended prioritising ‘actions related to health promotion of children and adolescents’. ‘We look forward to assessing how to adapt the policy recommendations for England to the rest of the world,’ says R ü diger Krech, director of the World Health Organization department of ethics, equity, trade and human rights. He argues that giving every child the best start in life ‘is critical in setting the foundation for a lifetime of health and successful contribution to society’.

Introduction

In terms of children’s social and emotional development the pre-school period is a time of rapid change. The typical pre-schooler is swiftly acquiring social skills, and these skills are developed and refi ned in play and friendships established with other children. At the same time the child is beginning to identify more strongly with parents and friends of the same sex.

The nature of family life is also changing dramatically. At this time in the family life-cycle a second child may be making their presence felt. Parents may find that the first child is experiencing some difficulties understanding how to share their parents’ love and they may witness regressive behaviour, such as thumb-sucking, bed-wetting or other behavioural manifestations of the child’s conflict.

This chapter considers various theoretical approaches to understanding the preschooler’s social and emotional development. Theory provides a basis for exploring issues relevant to this period of the child’s life and this stage of the family life-cycle, the child’s developing sense of self, confl ict, school adjustment, child abuse and bullying. Sibling relationships are discussed in the family life-cycle: 14.

1. ‘He sorted out those of the largest size’

2. ‘I weep for you,’ the Walrus said

3. ‘I deeply sympathise.’

4. With sobs and tears he sorted out

5. Those of the largest size,

6. Holding his handkerchief

7. Before his streaming eyes.

8. Lewis Carroll, Through the Looking Glass

Introduction

As noted by Adolph and Robinson any discussion of growth and development tends to focus on the organism’s progress from beginning to end and there is a paucity of research into what underpins or drives this change.

Everyone understands in a general way what is meant by growth. You only have to walk into a nursery or school and see the wall charts that enable parents or teachers to assess the heights of children. Listening in on any conversation between parents and grandparents about a grandchild will also generally reveal a reference to the child’s growth at some point.

The British Medical Dictionary defines growth as ‘the progressive development of a living being or part of an organism from its earliest stage to maturation including the attendant increase in size’. In the same dictionary the defi nition of development is ‘the series of changes by which the individual embryo becomes a mature organism’.

For the past 20 years we have lived through the information revolution, powered by the explosive growth of semiconductor integration and of the internet. The exponential performance improvement of semiconductor devices was predicted by Moore's law as early as the 1960s. There are several formulations of Moore's law. One of them is directed at the computing power of microprocessors. Moore's law predicts that the computing power of microprocessors will double every 18–24 months at constant cost so that their cost-effectiveness (the ratio between performance and cost) will grow at an exponential rate. It has been observed that the computing power of entire systems also grows at the same pace. This law has endured the test of time and still remains valid today. This law will be tested repeatedly, both now and in the future, as many people see today strong evidence that the “end of the ride” is near, mostly because the miniaturization of CMOS technology is fast reaching its limit, the so-called CMOS endpoint.

Besides semiconductor technology, improved chip designs have also fueled the phenomenal performance growth of microprocessors over the years. Historically, with each new process generation, the logic switching speed and the amount of on-chip logic have both increased dramatically. Faster switching speeds lead to higher clock rates. Aggressive chip designs also contribute to higher clock rates by improving the design of circuits or by pipelining the steps in the execution of an instruction.

Introduction

1. I am not yet born; provide me

2. With water to dandle me, grass to grow for me, trees to talk

3. To me, sky to sing to me, birds and a white light

4. In the back of my mind to guide me.

5. Louis MacNiece, ‘Prayer before birth’

As reflected in the poem by Louis MacNiece and as discussed in this text there are a range of theories that attempt to account for how we grow and develop as we do and to identify the optimal conditions under which development thrives. Issues that have occupied a great deal of time and attention, such as the genetics–environment debate, have undergone considerable refi nement. The shortcomings of simplistic neuromaturational views have been identifi ed in the light of more refi ned understanding that developmental change is more likely to emerge from context-dependent dynamic interactions of multiple factors and not through a single cause.