linux-kernel - Re: disabling group leader perf

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Date:	Mon, 06 Sep 2010 20:55:54 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Pekka Enberg <penberg@...helsinki.fi>,
	Tom Zanussi <tzanussi@...il.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-perf-users@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: disabling group leader perf_event

  On 09/06/2010 06:47 PM, Ingo Molnar wrote:
>
>> The actual language doesn't really matter.
> There are 3 basic categories:
>
>   1- Most (least abstract) specific code: a block of bytecode in the form
>      of a simplified, executable, kernel-checked x86 machine code block -
>      this is also the fastest form. [yes, this is actually possible.]

Do you then recompile it?  x86 is quite unpleasant.

>   2- Least specific (most abstract) code: A subset/sideset of C - as it's
>      the most kernel-developer-trustable/debuggable form.
>
>   3- Everything else little more than a dot on the spectrum between the
>      first two points.
>
> I lean towards #2 - but #1 looks interesting too. #3 is distinctly
> uninteresting as it cannot be as fast as #1 and cannot be as convenient
> as #2.

Curious - how do you guarantee safety of #1 or even #2?  Can you point 
me to any research?

Everything I'm aware of is bytecode with explicit measures to prevent 
forged pointers, but I admit I've spent no time on it.  It's interesting 
stuff, though.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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