Aca Important Questions 2 Marks 16marks

ADVANCED COMPUTER ARCHITECTURE TWO MARK QUESTIONS UNIT I INSTRUCTION LEVEL PARALLELISM TWO MARKS 1. List the various data dependence. Data dependence ,Name dependence, Control Dependence 2. What is Instruction Level Parallelism? Pipelining is used to overlap the execution of instructions and improve performance. This potential overlap among instructions is called instruction level parallelism (ILP) since the instruction can be evaluated in parallel. 3. Give an example of control dependence? if p1 {s1;} if p2 {s2;} S1 is control dependent on p1, and s2 is control dependent on p2. 4. What is the limitation of the simple pipelining technique? These technique uses in-order instruction issue and execution. Instructions are issued in program order, and if an instruction is stalled in the pipeline, no later instructions can proceed. 5. Briefly explain the idea behind using reservation station? Reservation station fetches and buffers an operand as soon as available, eliminating the need to get the operand from a register. 6. Give an example for data dependence. Loop: L.D F0,0(R1) ADD.D F4,F0,F2 S.D F4,0(R1) DADDUI R1,R1,#-8 BNE R1,R2, loop 7. Explain the idea behind dynamic scheduling? In dynamic scheduling the hardware rearranges the instruction execution to reduce the stalls while maintaining data flow and exception behavior.

8. Mention the advantages of using dynamic scheduling? It enables handling some cases when dependences are unknown at compile time and it simplifies the compiler. It allows code that was compiled with one pipeline in mind run efficiently on a different pipeline. 9. What are the possibilities for imprecise exception? The pipeline may have already completed instructions that are later in program order than instruction causing exception. The pipeline may have not yet completed some instructions that are earlier in program order than the instructions causing exception. 10. What are multilevel branch predictors? These predictors use several levels of branch-prediction tables together with an algorithm for choosing among the multiple predictors. 11. What are branch-target buffers? To reduce the branch penalty we need to know from what address to fetch by end of IF (instruction fetch). A branch prediction cache that stores the predicted address for the next instruction after a branch is called a branch-target buffer or branch target cache. 12. Briefly explain the goal of multiple-issue processor? The goal of multiple issue processors is to allow multiple instructions to issue in a clock cycle. They come in two flavors: superscalar processors and VLIW processors. 13. What is speculation? Speculation allows execution of instruction before control dependences are resolved. 14. Mention the purpose of using Branch history table? It is a small memory indexed by the lower portion of the address of the branch instruction. The memory contains a bit that says whether the branch was recently taken or not. 15. What are super scalar processors? Superscalar processors issue varying number of instructions per clock and are either statically scheduled or dynamically scheduled.

16. Mention the idea behind hardware-based speculation? It combines three key ideas: dynamic branch prediction to choose which instruction to execute, speculation to allow the execution of instructions before control dependences are resolved and dynamic scheduling to deal with the scheduling of different combinations of basic blocks. 17. What are the fields in the ROB?    

Instruction type Destination field Value field Ready field

18. How many branch selected entries are in a (2,2) predictors that has a total of 8K bits in a prediction buffer? 22 x 2 x number of prediction entries selected by the branch = 8K number of prediction entries selected by the branch = 1K 19. What is the advantage of using instruction type field in ROB? The instruction field specifies whether instruction is a branch or a store or a register operation 20. Mention the advantage of using tournament based predictors? The advantage of tournament predictor is its ability to select the right predictor for right branch.

UNIT II MULTIPLE ISSUE PROCESSORS 1.What is loop unrolling? A simple scheme for increasing the number of instructions relative to the branch and overhead instructions is loop unrolling. Unrolling simply replicates the loop body multiple times, adjusting the loop termination code. 2.When static branch predictors are used? They are used in processors where the expectation is that the branch behavior is highly predictable at compile time. Static predictors are also used to assists dynamic predictors. 3.Mention the different methods to predict branch behavior? Predict the branch as taken Predict on basis of branch direction (either forward or backward) Predict using profile information collected from earlier runs.

4. Explain the VLIW approach? They uses multiple, independent functional units. Rather than attempting to issue multiple, independent instructions to the units, a VLIW packages the multiple operations into one very long instruction. 5. Mention the techniques to compact the code size in instructions? Using encoding techniques Compress the instruction in main memory and expand them when they are read into the cache or are decoded. 6. Mention the advantage of using multiple issue processor?   

They are less expensive. They have cache based memory system. More parallelism.

7. What are loop carried dependence? They focuses on determining whether data accesses in later iterations are dependent on data values produced in earlier iterations; such a dependence is called loop carried dependence. e.g for(i=1000;i>0;i=i-1) x[i]=x[i]+s; 8. Mention the tasks involved in finding dependences in instructions? Good scheduling of code. Determining which loops might contain parallelism Eliminating name dependence 9. Use the G.C.D test to determine whether dependence exists in the following loop: for(i=1;i R ordering ,,, W->W ordering ,,,,, R->W and R-> R ordering. 21. What is multi threading? Multithreading allows multiple threads to share the functional uits of the single processor in an overlapping fashion. 22. What is fine grained multithreading? It switches between threads on each instruction, causing the execution of multiple threads to be interleaved. 23. What is coarse grained multithreading? It switches threads only on costly stalls. Thus it is much less likely to slow down the execution of an individual thread. UNIT V MULTI CORE ARCHITECTURE 1.What is multi threading? Multithreading allows multiple threads to share the functional uits of the single processor in an overlapping fashion. 2. What is fine grained multithreading? It switches between threads on each instruction, causing the execution of multiple threads to be interleaved. 3. What is coarse grained multithreading? It switches threads only on costly stalls. Thus it is much less likely to slow down the execution of an individual thread. 4.Advantages of multithreading  

If a thread gets a lot of cache misses the other threads can continue Fater execution

 

If a thread cannot use all the computing resources of the cpu running another thread permits to not leave these idle If several threads work on the same set of data they can actually share their cache .leading to better cache usage or synchroniation on its values

5.write disadvantages of multithreading   

It can interfere with each other when sharing hardware resources . Execution times are not improved but can be degraded. Hardware support for multithreading is more visible to software thus requiring more changes to both application programs and operating systems than multi threading

6.what is CMP CMP represents chip multi Processor also called multi core microprocessors .large uniprocessors are no longer scaling in performance,because it is only possible to extract a limited amount of parllelism from a techniques. 7.what is SMT. SMT means simultaneous multithreading .it is a technique for improving the overall efficiency of superscalar cpus with hardware multithreading .SMT permits multiple independent threads of execution to better utilize the resources provided by modern processors architectures. 8.what are the disadvantages of SMT    

It cannot improve the performance if any of the shared resources are limilted bottlenecks for the performance. Applications are run slower when multithreading is enabled. critics argue that is a considerable burden to put on the software developers that they have to test whetheir simultaneous multithreading it is good or bad for their application situations and insert extra logic to turn it off if it decreases performance.

9.what are types of multithreading  

Block multithreading Interleaved multithreading

10.advantages of CMP   

Smaller less complex cores onto a single chip Dynamically switching between cores and powering down unused cores Increased throughput performance by exploiting parallelism

11.what is multi core It is a design in which a single physical processor contains the core logic of more than one processor.it’s as if an intel xenon processor were opened up and inside were packaged all the circuitry and logic for two intel xenon processors. Tme multicore design takes several processor cores and packages them as a single physical processor .the goal of this design is to enable a system to run more tasks simultaneously and thereby achieve greater overall system performance.

UNIT I INSTRUCTION LEVEL PARALLELISM 16 MARKS FIRST PART 1. What is instruction-level parallelism? Explain in details about the various dependences and hazards caused in ILP?  



Define ILP Various dependences include – 1. Data dependence, 2. Name dependence and 3. control dependence. Hazards include1. Definition 2. Types of hazards and explain each one

2.Explain in detail about hardware approaches   

Define reservation stations Explain tomasulo’s algorithm and it’s stages Define reservation station components

3. Discuss about tomasulo’s algorithm to over come data hazard using dynamic scheduling?    

Dynamic scheduling with an example. How data hazard is caused. Architecture Reservation station. Examples of tomasulo’s algorithm

4. Explain how hardware based speculation is used to overcome control dependence? Ideas in hardware based speculation –   

dynamic scheduling, speculation, dynamic branch prediction. Architecture and example Reorder buffer. SECOND PART

5. Explain how to reduce branch cost with dynamic hardware prediction?   

Basic branch prediction and prediction buffers Correlating branch predictors Tournament based predictors

6.Explain compiler techniques for exposing ILP?   

Basic pipeline scheduling and loop unrolling Summary of Loop unrolling and scheduling technique Example

UNIT II MULTIPLE ISSUE PROCESSORS FIRST PART 1.Discuss about the VLIW approach?    

VLIW approach basic idea. Limitations and Principleof VLIW. Architecture of VLIW Advantages and disadvantages of VLIW

2.Explain the different techniques to exploit and expose more parallelism using compiler support? 



Loop-Level parallelism  Classifications of data dependences in loop  Finding affine index and multidimentional index and examples Software pipelining Global code scheduling – Trace scheduling and superblocks.

3. Explain how hardware support for exposing more parallelism at compile time?  

Conditional or predicated instructions Compiler speculation with hardware support SECOND PART

4. Differentiate hardware and software speculation mechanisms?  

Control flow Exception conditions Bookkeeping

5.Explain Intel IA-64 Architecture in detail with suitable reference to Itanium processor     

Intel IA-64 Instruction set Architecture Instruction format and support for exploit parallelism Prediction and speculation support Itanium processors Functional units and instruction issues

6. Explain the limitations of ILP     

Hardware model Window size and maximum issue count Realistic branch and jump prediction Effects of finite registers Effects of imperfect alias analysis

UNIT III MULTIPROCESSORS AND THREAD LEVEL PARALLELISM FIRST PART 1.Explainan about Taxonomy of parallel architecture?   

Idea Classification of Taxonomy of parallel architecture Flynns taxonomy  Classification based on the memory arrangement  Classification based on communication  Classification based on kind of parallelism Data parallel Functional parallel

2.Explain the snooping protocol or write invalidated protocol or centralized protocol or symmetric shared memory architecture with a state diagram?    

Basic schemes for enforcing cache coherence Cache coherence – definition Snooping protocol An example protocol – state diagram

3.Explain the directory based protocol or distributed shared memory architecture with a state diagram? Directory based cache coherence protocol – basics Example directory protocol 4.Explain relavant graphs ,dicuss the performance of symmetric shared memory multiprocessors  

Twp types of Coherent misses and examples Three application of workloads  Performance measurements commercial workloads  Multiprogramming and os worklaod  Performance of multiprogramming and os workload

5.Explain relavant graph ,discuss the performance of distributed shared memory multiprocessors    

Directory based performance Miss rate vs num processors Miss rate vs cache size Data miss rate versus block size SECOND PART

6.Define synchronization and explain the different mechanisms employed for synchronization among processors?   

Basic hardware primitive Implementing locks using coherence Barrier synchronization Hardware and software implementation

7.Discuss about the different models for memory consistency?  

Sequential consistency model Relaxed consistency model

8.How is multithreading used to exploit thread level parallelism within a processor? Multithreading – definition   

Fine grained multithreading Coarse grained multithreading Simultaneous multithreading

UNIT IV MEMORY AND I/O FIRST PART 1.Explain in detail about cache performance?   

Average memory access time and processor performance Miss penalty and out of order execution processors Improving cache performance

2. Explain the different technique to reduce cache miss penalty?   

Multiple caches Critical word first and early restart Giving priority to read misses over writes.



Merging write buffers Victim caches

3.Explain the different technique to reduce miss rate?    

Larger block size Larger caches Higher associativity Way prediction and pseudo associative caches Compiler optimization

4.Explain the different technique to reduce miss rate?   

3C’s of cache miss Division of conflict misses Techniques to reduce miss rate

5.Discuss how main memory is organized to improve performance?   

Wider main memory Simple interleaved memory Independent memory banks SECON PART

6.Explain the various levels of RAID?   

No redundancy Mirroring Bit-interleaved parity Block- interleaved parity P+Q redundancy

7.Explain the various ways to measure I/O performance?  

Throughput versus response time Little queuing theory

8. Explain various types of storage systems     

Magnetic devices Optical disks Magnetic tapes Automated tape libraries Flash memory

9.Examples of I/O Design performance measures  

Naïve design and cost performance Calculate poor performance of naïve design and calculate MTTF Value of naïve design



Calculate performance time for first step

UNIT V MULTICORE ARCHITECTURE FIRST PART

1.Explain in detail about hardware multithreading techniques?   

Fine grained multithreading Coarse grained multithreading Simultaneous multithreading

2.Explain in detail about CMP Architecture and SMT Architecture?  

Design challenges in SMT Potential performance advantage from SMT

3.Explain in detail about issues of CMP and SMT Architecture?         

Why are Design issues important? Why Multithreading Today Design Challenges Of SMT Reason for loss of throughput? And Design Challenges Transient Faults and Fault Detection via SMT Simultaneous & Redundantly Threaded Processor (SRT) and SRT Design Challenges Transient Fault Detection in CMPs Transient Fault Recovery for CMPs To maximize SMT performance

SECOND PART 4.Explain in detail about Intel Multi Core Architecture? 5.Describe in detail about SUN CMP architecture 6.Discuss in detail about heterogneous multi core processors 7.Explain about IBM Cell Processor?