linux-kernel - Re: [PATCH 1/8] perf: add PMU_RANGE_ATTR() helper for use by sw-like pmus

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Date:	Sat,  1 Feb 2014 16:58:05 +1100 (EST)
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Cody P Schafer <cody@...ux.vnet.ibm.com>,
	Linux PPC <linuxppc-dev@...ts.ozlabs.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Cody P Schafer <cody@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/8] perf: add PMU_RANGE_ATTR() helper for use by sw-like pmus

On Thu, 2014-16-01 at 23:53:47 UTC, Cody P Schafer wrote:
> Add PMU_RANGE_ATTR() and PMU_RANGE_RESV() (for reserved areas) which
> generate functions to extract the relevent bits from
> event->attr.config{,1,2} for use by sw-like pmus where the
> 'config{,1,2}' values don't map directly to hardware registers.

This is neat.

The split of the macros is a bit weird, ie. PMU_RANGE_RESV() doesn't really do
what it's name suggests.

I think you want one macro which creates the accessors, with a name that
reflects that - yeah I can't think of a good one right now, but "event" should
probably be in there because that's what it operates on.

Having a macro for the reserved regions is good, but you MUST actually check
that the reserved regions are zero. Otherwise you are permitting your caller to
pass junk in there and you then can't unreserved them in a future version of
the API.

So I think a macro that gives you a special reserved region routine would be
good, so you can write something like:

  if (event_check_reserved1() || event_check_reserved2())
  	return -EINVAL;

cheers
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