linux-kernel - Re: disabling group leader perf

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Message-ID: <20100906164824.339cd82e@lxorguk.ukuu.org.uk>
Date:	Mon, 6 Sep 2010 16:48:24 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Avi Kivity <avi@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, 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

> No, I want the ability to terminate the code at any time and clean up 
> any resources used.  We have exactly the same requirements for ordinary 
> userspace.

So you intend to prevent its use at any point where we have a kernel only
resource held in any way manner or form ? Remember we don't hold locks or
many kinds of kernel resource across syscalls. Likewise I'm interested
how you will keep it compatible with real time ?

> > - bounded memory use
> > - trustable behaviour for access
> 
> Right.
> 
> > and usually minimal side effects since you want to optimise very
> > heavily and side effects stop that (which is also why Fortran still kicks
> > C's backside for crunching)
> >
> > Not sure you need/want to do the conversion in kernel.
> 
> I prefer bytecode as well.
> 
> > I'd have thought a
> > sane way to handle it would have been to throw stuff at the kernel in
> > some kind of semi-sane byte code that can be interpreted by a noddy
> > interpreter but firstly when you get it have the kernel try and run a
> > helper to compile it.
> 
> So you do want to jit?

Depends what you mean by jit. JIT normally implies compiling/recompiling
as you go. Do we want to compile it once at load time - probably,
assuming the tool is present.
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