linux-kernel - Re: [PATCH 3/3 v2] perf tool: give user better message if precise is not supported

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Date:	Mon, 17 Sep 2012 09:11:13 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	David Ahern <dsahern@...il.com>, linux-kernel@...r.kernel.org,
	Robert Richter <robert.richter@....com>
Subject: Re: [PATCH 3/3 v2] perf tool: give user better message if precise is
 not supported


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Fri, 2012-09-14 at 22:11 +0200, Ingo Molnar wrote:
> >   return -EPERF_CPU_PRECISE_EV_NOTSUPP;
> 
> I just don't like having to enumerate all possible fails, I'm 
> too lazy. Can't we be smarter about that? Could we do a 
> {reason}x{bit-offset} like thing?
> 
> Where we limit reason to a few simple things like:
> 
>  invalid
>  out-of-range
>  not-supported
> 
> and have the bit-offset indicate the field we're having the particular
> problem with?
> 
> Then all we need is a smart way to generate and map the bit-offsets
> without too much manual labour. 

Putting the 'where' into a separate field would do that, and 
thus we could generate and report such structured errors as well 
- but nevertheless there will always be special/individual 
errors as well that won't fit into such a scheme, for which we 
should include a 'boring' errno range as well ...

I.e. a {where},{what} s32 pair of fields - if 'where' is zero 
then 'what' is the enumerated errno value I suggested, if it's 
nonzero then it's the 'where' indication you suggested.

Thanks,

	Ingo
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