svn commit: r274739 - head/sys/mips/conf

[Warner Losh]

> On Nov 25, 2014, at 12:57 AM, Mark R V Murray <mark at grondar.org> wrote:
> 
> 
>> On 24 Nov 2014, at 23:22, Warner Losh <imp at bsdimp.com> wrote:
>> 
>> What’s the minimum specs required for get_cyclecount()? Not all of the
>> boxes that Ian was posting about have high-resolution time-keeping counters
>> in hardware… Maybe there’s some underlying expectation for this function
>> that these systems either aren’t providing or can’t provide.
> 
> get_cyclecount should be a high-resolution timing counter linear in time, with a minimum tick no more accurate than a single instruction execution. In practice we take what we can get. It is used to measure hopefully chaotic events in order to obtain environmental entropy.

So right. armv6 and mips have something akin to that, but IIRC, not all arm v4/5 boxes can do much better than microseconds…

Warner

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