On Thu, 07 Apr 2011, Benjamin Herrenschmidt wrote:

quoted

quoted

Doesn't that mean that power_pmu_read() can only ever increase the value of
the perf_event and so will essentially -stop- once the counter rolls over ?

Similar comments every where you do this type of comparison.

Cheers,
Ben.

Sorry for the nag, but am I missing something about the way the register and
the previous values are reset in the overflow interrupt handler?

Well, not all counters get interrupts right ? Some counters are just
free running... I'm not sure when that power_pmu_read() function is
actually used by the core, I'm not that familiar with perf, but I'd say
better safe than sorry. When comparing counter values, doing in a way
that is generally safe vs. wraparounds. Eventually do a helper for that.

Cheers,
Ben.

I am honestly not sure, I was under the assumption that all counters would
generate an interrupt if they overflowed.  I do not have the hardware docs to
prove this, so I will have a V3 that (I think/hope) addresses your concerns out
momentarily.

Eric