linux-kernel - Re: [patch/rfc] perf on raspberry-pi without overflow interrupt

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Message-ID: <20140116173110.GA9655@laptop.programming.kicks-ass.net>
Date:	Thu, 16 Jan 2014 18:31:10 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	Will Deacon <will.deacon@....com>,
	Chad Paradis <chad.paradis@...t.maine.edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Stephane Eranian <eranian@...il.com>
Subject: Re: [patch/rfc] perf on raspberry-pi without overflow interrupt

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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