From: Rusty Russell <rusty@rustcorp.com.au>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>,
Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Zwane Mwaikambo <zwane@arm.linux.org.uk>,
Nathan Lynch <nathanl@austin.ibm.com>,
Joel Schopp <jschopp@austin.ibm.com>,
Ashok Raj <ashok.raj@intel.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
Gautham R Shenoy <ego@in.ibm.com>,
akpm@linux-foundation.org, Dipankar <dipankar@in.ibm.com>
Subject: Re: CPU hotplug: system hang on CPU hot remove during `pfmon --system-wide'
Date: Wed, 30 May 2007 12:42:01 +1000 [thread overview]
Message-ID: <1180492921.30202.77.camel@localhost.localdomain> (raw)
In-Reply-To: <alpine.LFD.0.98.0705291347320.26602@woody.linux-foundation.org>
On Tue, 2007-05-29 at 13:56 -0700, Linus Torvalds wrote:
>
> On Mon, 28 May 2007, Srivatsa Vaddagiri wrote:
> >
> > So is it settled now on what approach we are going to follow (freezer
> > vs lock based) for cpu hotplug? I thought that Linus was not favouring freezer
> > based approach sometime back ..
>
> As far as I'm concerned, we should
> - use "preempt_disable()" to protect against CPU's coming and going
> - use "stop_machine()" or similar that already honors preemption, and
> which I trust a whole lot more than freezer.
> - .. especially since this is already how we are supposed to be protected
> against CPU's going away, and we've already started doing that (for an
> example of this, see things like e18f3ffb9c from Andrew)
Indeed, this is how it was supposed to work.
Note that it is possible to make stop_machine() an even larger hammer,
by scheduler mods to flush all the preempted tasks. This would drop the
requirement for preempt_disable().
But cute as that would be, I've been waiting until someone demonstrates
an actual need...
Rusty.
next prev parent reply other threads:[~2007-05-30 2:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-28 1:54 CPU hotplug: system hang on CPU hot remove during `pfmon --system-wide' Satoru Takeuchi
2007-05-28 6:55 ` Srivatsa Vaddagiri
2007-05-29 20:56 ` Linus Torvalds
2007-05-30 2:42 ` Rusty Russell [this message]
2007-05-30 16:55 ` Srivatsa Vaddagiri
2007-05-30 17:03 ` Linus Torvalds
2007-05-31 16:51 ` Srivatsa Vaddagiri
2007-06-06 15:24 ` Gautham R Shenoy
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