Control Hazards

Duration: 4 min

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Module outline

  1. Quantitative Aptitude: Ratio and Proportion (Ratios), Data Interpretation, Mixture and Alligation, Permutation and Combination, Number System, Sequence and Series (Series), Speed Time and Distance, Speed Mathematics and Basic Mathematics, Algebra, Percentage, Profit and Loss, Simple Interest and Compound Interest, Powers and Exponents (Surds and Indices), Time and Work, Mensuration and Geometry, Partnership
  2. Reasoning Ability: Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Data Sufficiency, Seating Arrangements, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Directions (Direction Test), Ranking, Order and Sequence, Syllogisms, Blood Relations, Puzzle Solving (Puzzles), Inequality, Machine Input-Output
  3. English Language: Vocabulary, Noun, Subject Verb Agreement (Verb Noun Agreement), Adjectives, Tenses, Comprehension / Reading Comprehension / Unseen Passages (Critical Reasoning) (Paragraph Questions), Cloze Test (Cloze Passage), Sentence Correction (Error Correction), Sentence Completion (Fill in the blanks), Sentence Re-arrangements (Para Jumbles) (Narrative Sequencing), Sentence Construction, Pronoun, Preposition, Conjunction, Adverb, Verb, Modals, Articles, Determiner, Interjection
  4. General Awareness: Evolution of Indian Banking (Banking & Financial Awareness), GK- Current Affairs, Static General Knowledge, Indian Economy
  5. C Concepts + MCQs (IT Specialist): C Programming by Yash Sir, C Language Core
  6. Java (IT Specialist): Java
  7. Python (IT Specialist): Python for Placements by Yash Sir, Python Basics
  8. OOPs (IT Specialist): Object Oriented Programming (OOPS)
  9. DBMS (IT Specialist): Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, File Organization & Indexing, Relational Algebra, Relational Calculus, Transaction Management, Concurrency Control, Database Recovery, ORDBMS, Database Security & Authorization, Query Processing & Optimization, Enhanced Data Models, Data Warehousing & Mining, Big Data Systems, NoSQL
  10. SQL (IT Specialist): SQL
  11. Software Engineering (IT Specialist): Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  12. Data Structure (IT Specialist): Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing
  13. Operating System (IT Specialist): Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Deadlock, Threads & Process Creation, Memory Management, Virtual Memory, Disc Scheduling, File Management, Windows OS, Linux OS, Security, Distributed Systems, Virtual Machines
  14. Compiler Design (IT Specialist): Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization, Run Time Environment
  15. Computer Architecture (IT Specialist): Basics of COA, Floating Point Rep, Cache Memory Organization, Input Output Organisation, Pipelining, Instr Formats & Modes, Control Unit Design, Register Transfer and Microoperations, Multiprocessors, Programming the Basic Computer
  16. Data Communication & Networking (IT Specialist): Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, DLL: Error Control, DLL: Framing, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics, Network Security
  17. Descriptive Test (Main Exam): English Writing Ability
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

The lecture focuses on Control Hazards in pipelined processors, specifically addressing the inefficiencies caused by branch instructions. The instructor explains that when a branch instruction is encountered, the processor may have already fetched and partially executed subsequent instructions that turn out to be incorrect. This leads to a 'hazard' where these instructions must be discarded. The session transitions into a quantitative analysis, teaching students how to calculate the Cycles Per Instruction (CPI) penalty based on the frequency of branch instructions and the number of stalls they incur.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The instructor begins by defining the problem of Control Hazards. He presents a scenario where instruction I1 is a branch, and the next instruction to execute is I10. However, the processor has already partially executed I1, I2, I3, which is the core problem. A flowchart is displayed, categorizing 'Branch Instruction' into 'Conditional' and 'Unconditional'. The 'Conditional' branch further splits into 'Condition true (Jump)' and 'Condition false (No Jump)'. The instructor writes a vertical sequence I1, I2, I3, I4, I5 to represent the instruction stream, emphasizing that the decision to jump is not immediate.

  2. 2:00 – 4:30 02:00-04:30

    The instructor visualizes the hazard using a pipeline timing diagram with stages IF, ID, EX, and WB. He marks I1 as the branch instruction and shows red crosses over I2 and I3 in the IF and ID stages, indicating they are flushed. He then introduces a calculation problem: 'Consider a system where 20% instruction are branch instruction... Find the CPI'. He calculates the CPI for three cases. Case 1: 1 Stall results in 0.8 x 1 + 0.2 x 2 = 1.2. Case 2: 2 Stalls results in 0.8 x 1 + 0.2 x 3 = 1.4. Case 3: 3 Stalls results in 0.8 x 1 + 0.2 x 4 = 1.6. This demonstrates how stall cycles directly increase the average CPI.

The lecture effectively bridges the gap between theoretical pipeline hazards and practical performance metrics. By first illustrating the structural problem of branch instructions wasting cycles through a flowchart and timing diagram, the instructor sets the stage for the mathematical solution. The calculation of CPI serves as a practical application, showing how a 20% branch frequency with varying stall penalties (1, 2, or 3 cycles) degrades performance from a base CPI of 1.0 to 1.2, 1.4, and 1.6 respectively. This progression helps students understand the tangible cost of control dependencies in processor design.

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