linux-kernel - Re: Porting "jump labels" to userspace

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Message-ID: <20110216203953.GB2015@Krystal>
Date:	Wed, 16 Feb 2011 15:39:53 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	Roland McGrath <roland@...hat.com>, Mark Wielaard <mjw@...hat.com>,
	Stefan Hajnoczi <stefanha@...il.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Julien Desfossez <julien.desfossez@...ymtl.ca>,
	dominique.toupin@...csson.com, ltt-dev@...ts.casi.polymtl.ca,
	systemtap@...rces.redhat.com, linux-kernel@...r.kernel.org,
	Jason Baron <jbaron@...hat.com>, hpa@...or.com,
	rostedt@...dmis.org, mingo@...e.hu, tglx@...utronix.de,
	andi@...stfloor.org, rth@...hat.com,
	masami.hiramatsu.pt@...achi.com, fweisbec@...il.com,
	avi@...hat.com, davem@...emloft.net, sam@...nborg.org,
	michael@...erman.id.au, Peter Zijlstra <peterz@...radead.org>
Subject: Re: Porting "jump labels" to userspace

* David Daney (ddaney@...iumnetworks.com) wrote:
> On 02/16/2011 12:04 PM, Roland McGrath wrote:
>> IMHO there is not really so much to the in-kernel implementation that it's
>> worth attempting to reuse the code in userland.  Pretty much all the work
>> is in the details of the implementation that would naturally differ a lot
>> in a different context.  If you understand the mechanism and the machine
>> details, then implementing it well for a userland context is not a big deal
>> and is cleaner to do from scratch than shoe-horning kernel-centric code
>> into a wildly different context.
>>
>
> Good point.
>
> Certainly the details of maintaining instruction cache coherency may be  
> different in userspace.

Indeed, the arch-specific parts will need some extra care (which might, in the
worse case scenario, require to suspend a whole process during the update), but
the generic code in jump_label.c and jump_label.h could certainly be reused.

Thanks,

Mathieu

>
> David Daney

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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