linux-kernel - Re: [PATCH 1/2] tools, perf: Add a precise event qualifier v2

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Message-ID: <20130723225150.GT6123@two.firstfloor.org>
Date:	Wed, 24 Jul 2013 00:51:50 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Vince Weaver <vince@...ter.net>
Cc:	Andi Kleen <ak@...ux.intel.com>, Andi Kleen <andi@...stfloor.org>,
	acme@...radead.org, mingo@...nel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	torvalds@...ux-foundation.org, trinity@...r.kernel.org
Subject: Re: [PATCH 1/2] tools, perf: Add a precise event qualifier v2

On Tue, Jul 23, 2013 at 05:27:43PM -0400, Vince Weaver wrote:
> 
> I hate having to justify why breaking the ABI is unacceptable.

Well it's a testing ABI, so we can do changes to it.

I hope you're not suggesting that perf cannot be extended anymore.
As you know, hardware PMUs are constantly evolving, and perf has evolve
along with them to stay useful.

> It breaks the ABI.  The events/* sysfs files are documented as only 
> holding values for the bitfields described in format/*.

Ok. Need to fix the documentation then for precise=1.  I'll send patches.

Also can add it to format/*, but since it's not in config* it will
be an extension. Since it would be awkward to teach every parser
about all the flags, we could add a "flags" field that is handled 
like config, and contains all the flags.

So format/precise would be 

flags:15-16

on little endian. Looks good?

> I'm a bit grumpy about this because I just finished fixing the fallout 
> from your last time breaking the ABI a few weeks ago when your broken code 
> started dumping non-hex fields into the sysfs event strings.  I've learned 

Not sure what you're talking about?

iirc the only recent sysfs change of mine merged recently was adding
intx/intx_cp, and format files never have had hex numbers in it.

> now that I have to go over your patches with a fine-tooth code because you 
> have no regard for the ABI.

Any useful code review is appreciated.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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