The operator of a warehouse scale computer may be interested in increasing

The operator of a warehouse scale computer may be

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The operator of a warehouse-scale computer may be interested in increasing throughput the total amount of work done in a given time.
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45 Measuring, Reporting, and Summarizing Performance The phrase “the throughput of X is 1.3 times higher than Y” signifies here that the number of tasks completed per unit time on computer X is 1.3 times the number completed on Y.
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46 Measuring, Reporting, and Summarizing Performance Execution Time Wall-clock time, response time, or elapsed time, which is the latency to complete a task, including disk accesses, memory accesses, input/output activities, operating system over-head everything. With multiprogramming, the processor works on another program while waiting for I/O and may not necessarily minimize the elapsed time of one program.
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47 Measuring, Reporting, and Summarizing Performance CPU time recognizes this distinction and means the time the processor is computing, not including the time waiting for I/O or running other programs. To evaluate a new system the users would simply compare the execution time of their workloads the mixture of programs and operating system commands that users run on a computer.
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48 Compute Speedup – Amdahl’s Law Amdahl’s law states that the performance improvement to be gained from using some faster mode of execution is limited by the fraction of the time the faster mode can be used. Amdahl’s law defines the speedup that can be gained by using a particular feature.
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49 Compute Speedup – Amdahl’s Law The fraction of the computation time in the original computer that can be converted to take advantage of the enhancement. For example, if 20 seconds of the execution time of a program that takes 60 seconds in total can use an enhancement, the fraction is 20/60. This value, which we will call Fraction enhanced , is always less than or equal to 1.
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50 Compute Speedup – Amdahl’s Law The improvement gained by the enhanced execution mode, that is, how much faster the task would run if the enhanced mode were used for the entire program This value is the time of the original mode over the time of the enhanced mode. If the enhanced mode takes, say, 2 seconds for a portion of the program, while it is 5 seconds in the original mode, the improvement is 5/2. We will call this value, which is always greater than 1, Speedup enhanced .
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51 Compute Speedup – Amdahl’s Law Speedup is due to enhancement(E): Time Before Time After Let F be the fraction where enhancement is applied => Also, called parallel fraction and (1-F) as the serial fraction = E x Time before x [(1-F) + F S ] Speedup(E) = E x Time before E x Time after = 1 F S ] [(1-F) + Execution time after
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52 Principles of Computer Design The Processor Performance Equation Principles
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53 Principles of Computer Design Principles Different instruction types having different CPIs
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54 Example Instruction mix of a RISC architecture.
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  • Fall '19
  • Central processing unit, CPU cache

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