Re: [RFC][PATCH 2/6] perf, arch: Rework perf_event_index()

[Will Deacon]

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).

> 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.

Will
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