Re: [PATCH] POWER: perf_event: Skip updating kernel counters ifregister value shrinks
From: Benjamin Herrenschmidt
Date: Thu Apr 07 2011 - 00:23:48 EST
> > 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.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/