linux-kernel - Re: [BUGFIX][PATCH] Freezer, CPU hotplug, x86 Microcode: Fix task freezing failures

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Message-ID: <20111004071508.GA15637@dhcp-172-17-108-109.mtv.corp.google.com>
Date:	Tue, 4 Oct 2011 00:15:08 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, tigran@...azian.fsnet.co.uk,
	tglx@...utronix.de, mingo@...e.hu, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [BUGFIX][PATCH] Freezer, CPU hotplug, x86 Microcode: Fix task
 freezing failures

Hello,

On Mon, Oct 03, 2011 at 10:47:54AM +0200, Borislav Petkov wrote:
> I think your patch makes sense because re-loading the ucode during
> a suspend/resume cycle is unnecessary. If one wants to update the
> microcode, it should happen later when the box is resumed again: you
> simply put the new microcode image in /lib/firmware/... and on AMD
> unload/reload the microcode module and on Intel you do either that or
> use the deprecated microcode_ctl.

I don't think it changes anything for suspend/resume cycles.  They're
different hooks.  The proposed patch changes actual cpu hotplug paths.

> However, let me test it on a couple of AMD boxes tomorrow to verify.
> 
> > At the moment I can't think of any clean solution that solves both these problems - 
> >   a. The problem of requesting microcode from userspace when it is frozen (which can be individually
> >      solved by my patch).
> >   b. The possible need for a revised microcode during CPU online (due to the remote usecase of 
> >      physically plugging-out and plugging-in a new CPU), when the tasks are frozen.
> 
> Yeah, let me remind you guys, we're talking about x86 CPUs here. AFAICT,
> I don't think that physical unplug is supported by any vendor yet but
> I'd welcome surprises :-).

I recall hearing about someone experimenting with actual hotplug a
while ago.  Dunno whether that was production or not tho.  Even if
not, given the continuing penetration of x86 into highend, I don't
think it would take too long to see physical CPU hotplug in
production.  Also, it just is a poor engineering.

Thanks.

--
tejun
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