The CPU Performance Equation

Structured Computer Organization (4th Edition)

Info icon This preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: The: EPIJ Parlor-manna Equltlnn Most computers are constructed using a clock running at a constant rate. These discrete time events are called ticks, stock ticks. stock periods, stocks. weir-s, or cfoei: eycies. Computer designers refer to the time of a clock period by its dura— tion (cg. 2 us) or by its rate (cg, SDI] MHz}. CPU time for aprogram can then he espresscd two ways: CPU time = CPU clock cycles for a pmgram at Elle-cit cycle time [if . _ CPUclockcyclesforaEy'mtt mum" Clockrate In addition to the number of cloclt cycles needed to execute a pmg'am, we can afso count the number of instructions executed—the instruction path length or in- struction cotter (HZ). If we know the number of clock cycles and the instruction count we can calculate the average number [If stock cycles per instruction {CPI}: CPI = CPU clock cycles for a my D: This CPU figure of merit provides insight into different styles of instruction sets and implementations, and we 1still use it extensively in the next four chapters. By transposing instruction count in the ahme formula, clock cycles can he de- fined as 1:: K CPI. "this allows us to use CPI in the execution time fonnula: CPU time = [CHEPTsfln-elteyelemue _ tescpi ”Um-m Expanding the first formula into the units of measure shows how the pieces fit together: Program Innh'uction K Clock cycle _ Program tnstrueuons H Clock cycles Seconds Somalis = CPU firrle As this formula demonstrates. CPU performance is dependent upon three charac— teristics: clock cycle {or rate), clock cycles per instmctiom and instruction count. Furfllenuore, CPU time is eqmtty dependent on these three characteristics: A 10% improvement in any one of Iltem leads to a 10% improvement in CPU time. MtPS cat“ Willlfi't’l 'WC’J-tum FEW Fetter-“Kl S H L I Clo-cl: nerE‘i PM “ geese cm ma ...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern