From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Eric B Munson <emunson@mgebm.net>
Cc: a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org,
paulus@samba.org, anton@samba.org, acme@ghostprotocols.net,
mingo@elte.hu, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] POWER: perf_event: Skip updating kernel counters if register value shrinks
Date: Thu, 07 Apr 2011 14:22:57 +1000 [thread overview]
Message-ID: <1302150177.2458.30.camel@pasglop> (raw)
In-Reply-To: <20110406212733.GB2596@mgebm.net>
> > 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.
next prev parent reply other threads:[~2011-04-07 4:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-25 13:28 [PATCH] POWER: perf_event: Skip updating kernel counters if register value shrinks Eric B Munson
2011-03-29 6:03 ` Benjamin Herrenschmidt
2011-03-29 14:25 ` Eric B Munson
2011-03-29 21:12 ` Benjamin Herrenschmidt
2011-03-30 18:36 ` Eric B Munson
2011-03-31 6:04 ` Benjamin Herrenschmidt
2011-03-31 16:14 ` Eric B Munson
2011-04-06 21:27 ` Eric B Munson
2011-04-07 4:22 ` Benjamin Herrenschmidt [this message]
2011-04-07 16:16 ` Eric B Munson
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