On 08/25/2011 07:19 AM, stephane eranian wrote:
> Hi,
> 
> Sorry for late reply.
> 
> The current support for mmaped count is broken on perf_event x86.
> It simply does not work. I think it only works on PPC at this point.

Just as an aside, you can access the counter registers from user space
on Power (aka PPC) machines, but because the kernel is free to schedule
the events onto whatever counters that meet the resource constraints,
it's not at all clear which hardware counter to read from user space,
and in fact, with event rotation, the counter being used can change from
one system tick till the next.

If you program a single event, you can be guaranteed that it won't move
around, but you still will have to guess or somehow determine which
hardware counter is being used by the kernel.

- Corey

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