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

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Tue, 2011-11-22 at 11:47 +0000, Will Deacon wrote:
> On Tue, Nov 22, 2011 at 11:26:20AM +0000, Peter Zijlstra wrote:
> > On Mon, 2011-11-21 at 22:43 +0000, Will Deacon wrote:
> > > Perhaps we could disable it while per-cpu events are running, although I
> > > think this will probably just lead to SIGILL central for anybody trying to
> > > use the counters in userspace.
> > 
> > One possibility would be to do as I did in patch 4, except ARM has it
> > disabled by default and the folks who think they know WTF they're doing
> > can enable it or so.
> 
> The problem is that everybody thinks they know WTF they're doing!

> But you know that the first thing people will do is zero the registers.

*groan*, fair enough ;-)

> > Also, for those ARMs that do have a user readable clock, you could
> > support the new time_{mult,shift,offset} from patch 5.
> 
> The user-readable clock will first appear in Cortex-A15, so the code for
> that still needs to hit mainline before I can look at doing this in perf.

OK, I had interpreted your "we don't always have" to be slightly more
common than just A15.