Anders Blomdell wrote: > The code looks OK, but if you hit some unsigned - signed - unsigned > conversion during wraparounds, the latencies experienced suggest that > you run a 1.5 GHz computer (or possibly a 3GHz, never get the 2^32 vs > 2^31 stuff right): > > 2^31/1.5 -> 1.4317e+09 Hz > > BTW: Why not use the 64 bit value from rdtsc (but storing the diff in a > 32 bit quantity to get the divide right in kernel space)?.
This was a rather good idea. I changed it in a way you suggested. Another problem was that I wrote something like: outb(...) rdtsc(start_time) Sometimes the ISR set up end_time before the start_time could be set. This was another problem. I just swapped the two lines above and reduced the measured time by the overhead which is incured by rdtsc(). The results look quite reasonable. Regards, Markus
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