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Message-ID: <1321907755.28118.30.camel@twins>
Subject: Re: [RFC][PATCH 2/6] perf, arch: Rework perf_event_index()
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Will Deacon <will.deacon@arm.com>
Cc: "mingo@elte.hu" <mingo@elte.hu>, William Cohen <wcohen@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        Paul Mundt <lethal@linux-sh.org>,
        "David S. Miller" <davem@davemloft.net>,
        Richard Kuo <rkuo@codeaurora.org>,
        Stephane Eranian <eranian@google.com>, Arun Sharma <asharma@fb.com>,
        Vince Weaver <vince@deater.net>
Date: Mon, 21 Nov 2011 21:35:55 +0100
In-Reply-To: <20111121203145.GA7301@mudshark.cambridge.arm.com>
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On Mon, 2011-11-21 at 20:31 +0000, Will Deacon wrote:
> On Mon, Nov 21, 2011 at 07:18:10PM +0000, Peter Zijlstra wrote:
> > But does ARM have a read PMU counter from userspace
> > instruction/capability?
> 
> In ARMv7, you can enable user access to the performance counters but the
> access is R/W so I don't think it's something we want to do (could interfere
> with another task doing system-wide profiling).

Yeah, write access is pushing it a bit.. 

> > Lacking that its all moot of course. If it does, it would be nice to
> > have an ARM version of patch 6.
> 
> Well we'd need a way to get around the all-or-nothing user access to the PMU
> and also the fact that we don't always have a user-readable clocksource.
> 
> Either way, the event counters are indexed from 0 on ARMv7 so we should
> use perf_event_idx_default.

Ok, done. Thanks!