22.6. Troubleshooting Processor Problems

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Processor performance is probably the most debated factor in system performance. Although it is true that a faster processor executes instructions faster, it can only execute about one instruction per clock cycle. When processor speed increases, other system component factors must be considered, in addition to their overall integration. For these reasons, a 3GHz processor is not exactly ten times faster than a 300MHz processor.

Further complicating the issue are multiprocessor systems. Two processors do not double the speed of the system, because both the operating system and application must be able to scale to the extra processor to leverage maximum performance from the system. As with processor speed, multiprocessor configurations do not increase speed geometrically.

Considering that processors sit idle most of the time, replacing a slower processor or adding a second one might not lead to the expected performance increase.

22.6.1 Evaluating the Processor Subsystem

Two useful counters in the Processor category of performance objects are % Interrupt Time and % Processor Time.

The % Interrupt Time counter indicates the percentage of time the processor spent receiving and servicing hardware interrupts during the sample interval. This value is an indirect indicator of the activity of devices that generate interrupts, such as the system clock, the mouse, disk drivers, data communication lines, NICs, and other peripheral devices. These devices normally interrupt the processor when they have completed a task or require attention. Normal thread execution is suspended during interrupts. Most system clocks interrupt the processor every 10 milliseconds, creating a background of interrupt activity. This counter displays the average busy time as a percentage of the sample time.

The % Processor Time counter indicates the percentage of time that the processor is executing a non-idle thread. This counter was designed as a primary indicator of processor activity. It is calculated by measuring the time that the processor spends executing the thread of the idle process in each sample interval, and subtracting that value from 100%. (Each processor has an idle thread that consumes cycles when no other threads are ready to run.) It can be viewed as the percentage of the sample interval spent doing useful work. This counter displays the average percentage of busy time observed during the sample interval. It is calculated by monitoring the time the service was inactive, and then subtracting that value from 100%.

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    HP ProLiant Servers AIS. Official Study Guide and Desk Reference
    HP ProLiant Servers AIS: Official Study Guide and Desk Reference
    ISBN: 0131467174
    EAN: 2147483647
    Year: 2004
    Pages: 278

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