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Message-ID: <1302150177.2458.30.camel@pasglop> Date: Thu, 07 Apr 2011 14:22:57 +1000 From: Benjamin Herrenschmidt <benh@...nel.crashing.org> To: Eric B Munson <emunson@...bm.net> Cc: a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...e.hu, acme@...stprotocols.net, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org, anton@...ba.org Subject: Re: [PATCH] POWER: perf_event: Skip updating kernel counters if register value shrinks > > 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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