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rAw

Cpu speed measuring

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My measuring routine fails. in win32 environment (which is multithread) it measures the speed of my cpu for about 500+/- 50 mhz (and it is p3-500). I''m using rdtsc instruction to get cpu cycle clock. HOW TO OMIT that mistake? routine alogorithm: a=timer(); for (; { b=timer(); if (b!=a) break; } b=a; c=rdtsc(); for (; { a=timer(); if (b!=a) break; } c=rdtsc-c; cpu_speed=c*1000; // the period of time in timer() function is 1/1000s

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You have to call a serializing CPU instruction (like cpuid) in order to get to-the-tick accurate readings, and need to make sure you''re not suffering from a cache miss penalty.

Also, time it for longer than 1ms - take at least 10 if not 100 or 1000. You can call Sleep(10), just make sure you start and end on a timer edge (like you do now) and divide by the time elapsed as indicated by the timer calls - don''t assume 1ms.

Magmai Kai Holmlor
- Not For Rent

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