From: Vince Weaver <vincent.weaver@maine.edu>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: perf: rdpmc and PERF_EVENT_IOC_RESET
Date: Thu, 18 Aug 2016 00:32:25 -0400 (EDT) [thread overview]
Message-ID: <alpine.DEB.2.20.1608180025420.8191@macbook-air> (raw)
In-Reply-To: <20160817152616.GT30192@twins.programming.kicks-ass.net>
On Wed, 17 Aug 2016, Peter Zijlstra wrote:
> Hurm.. I never considered using RESET with rdpmc(). The typical usage of
> rdpmc() I considered is something like:
I'm finally trying to hook up PAPI to properly use rdpmc and PAPI likes to
use IOC_RESET in various places. I can just special case to not do so
when in rdpmc mode, but I got curious if RESET was expected to work.
> But the rdpmc user function should:
> ...
>
> Which sign-extends the RDPMC result and adds it to userpg->offset,
> resulting in a positive number again.
I will have to check to see if PAPI is using the proper code.
What happens is the procesed result has bit 49 set for some reason, so the
results are 2^49 too big. I've been trying to track it down, but the PAPI
code is a bit of a mess (to put it mildly).
Vince
prev parent reply other threads:[~2016-08-18 4:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-17 4:53 Vince Weaver
2016-08-17 15:26 ` Peter Zijlstra
2016-08-18 4:32 ` Vince Weaver [this message]
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