linux-kernel - Re: [git pull for -mm] CPU isolation extensions (updated2)

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Message-ID: <Pine.LNX.4.58.0802122335530.30573@gandalf.stny.rr.com>
Date:	Wed, 13 Feb 2008 00:19:21 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
cc:	Max Krasnyansky <maxk@...lcomm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	torvalds@...ux-foundation.org, LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>, Paul Jackson <pj@....com>,
	gregkh@...e.de, Rusty Russell <rusty@...tcorp.com.au>,
	Oleg Nesterov <oleg@...sign.ru>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [git pull for -mm] CPU isolation extensions (updated2)

On Tue, 12 Feb 2008, Peter Zijlstra wrote:
> >
> > Rusty - Stop machine.
> >    After doing a bunch of testing last three days I actually downgraded stop machine
> >    changes from [highly experimental] to simply [experimental]. Pleas see this thread
> >    for more info: http://marc.info/?l=linux-kernel&m=120243837206248&w=2
> >    Short story is that I ran several insmod/rmmod workloads on live multi-core boxes
> >    with stop machine _completely_ disabled and did no see any issues. Rusty did not get
> >    a chance to reply yet, I hopping that we'll be able to make "stop machine" completely
> >    optional for some configurations.
>

This part really scares me. The comment that you say you have run several
insmod/rmmod workloads without kstop_machine doesn't mean that it is still
safe. A lot of races that things like this protect may only happen under
load once a month. But the fact that it happens at all is reason to have
the protection.

Before taking out any protection, please analyze it in detail and report
your findings why something is not needed. Not just some general hand
waving and "it doesn't crash on my box".

Besides that, kstop_machine may be used by other features that can have an
impact.

Again, if you have a system that cant handle things like kstop_machine,
than don't do things that require a kstop_machine run. All modules should
be loaded, and no new modules should be added when the system is
performing critical work. I see no reason for disabling kstop_machine.

-- Steve

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