mmio latency measurements

Segher Boessenkool segher at
Fri Jul 1 02:41:03 EST 2005

> On ppc64, there is no cycle-counter per-se, but a HW timebase that 
> ticks
> at a fixes frequency (independently of the CPU frequency nowadays).

On a 970, and presumably on POWER4 and maybe POWER5 as well,
you *can* get cycle counts -- from the performance monitor
counters.  Simply write 0xf00 to MMCR0 and then read the cycle
count from PMC1.


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