Date: Thu, 16 Jan 2014 18:31:10 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: Will Deacon <will.deacon@arm.com>,
        Chad Paradis <chad.paradis@umit.maine.edu>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Stephane Eranian <eranian@gmail.com>
Subject: Re: [patch/rfc] perf on raspberry-pi without overflow interrupt
Message-ID: <20140116173110.GA9655@laptop.programming.kicks-ass.net>
References: <alpine.DEB.2.10.1401081613370.4410@vincent-weaver-1.um.maine.edu>
 <20140108225315.GG31570@twins.programming.kicks-ass.net>
 <alpine.DEB.2.10.1401082245120.22965@vincent-weaver-1.um.maine.edu>
 <20140109101921.GA26435@mudshark.cambridge.arm.com>
 <alpine.DEB.2.10.1401092304590.31813@vincent-weaver-1.um.maine.edu>
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On Thu, Jan 16, 2014 at 12:13:10PM -0500, Vince Weaver wrote:
> On Tue, 14 Jan 2014, Peter Zijlstra wrote:
> 
> > On Mon, Jan 13, 2014 at 11:55:17PM -0500, Vince Weaver wrote:
> 
> > > I don't see an existing pmu capabilities struct... or do you mean
> > > coming up with one?
> > 
> > Yeah, adding one.
> 
> So would it be a struct, or just an integer with flags?

I hadn't really considered that; per the below proposed names I suppose
I was thinking of 'unsigned long flags' with #define PMU_HAS_flags. But
a named struct would work too I suppose.

> > > Would it only hold an "overflow_interrupt_available" flag, or are
> > > there other generic capabilities it would be handy to know about?
> > 
> > Possible (other) flags could be:
> > 
> >   PMU_HAS_INT      -- would allow sampling events
> >   PMU_HAS_PRECISE  -- would allow any ::precise value
> >   PMU_HAS_FILTER   -- would allow all os/user/etc. flags
> 
> should we export these to userspace somehow?
> 
> It would be handy to be able to tell you're getting EOPNOTSUP because
> PMU_HAS_INT is not set for your pmu, rather than trying to guess why 
> things are failing.

Yeah I suppose we could do something like that. Maybe something like:

# cat /sys/bus/event_source/devices/cpu/flags
int precise filter

?
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