From mboxrd@z Thu Jan  1 00:00:00 1970
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: Re: Xen 4.2 Release Plan / TODO
Date: Tue, 26 Jun 2012 17:09:06 -0400
Message-ID: <20120626210906.GA14905@phenom.dumpdata.com>
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	<20120626203151.GA8676@US-SEA-R8XVZTX>
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To: Matt Wilson <msw@amazon.com>
Cc: Ian Campbell <Ian.Campbell@citrix.com>, xen-devel <xen-devel@lists.xen.org>
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On Tue, Jun 26, 2012 at 01:31:51PM -0700, Matt Wilson wrote:
> On Tue, Jun 26, 2012 at 01:39:42AM -0700, Ian Campbell wrote:
> >     * [BUG] vcpu-set doesn't take effect on guest, reported by Intel:
> >       http://bugzilla.xen.org/bugzilla/show_bug.cgi?id=1822
> 
> This may be a problem with the guest, rather than a problem with Xen
> or the toolstack. I tested on a domU running a 3.2.20-based Linux
> kernel. The domU kernel didn't automatically enable the vCPUs after
> calling "xl vcpu-set" to increase the allocation.
> 
> # xl list 2
> Name                                        ID   Mem VCPUs      State Time(s)
> test                                         2 15360     1     -b---- 6617.6
> # xl vcpu-set 2 4
> # xl list 2
> Name                                        ID   Mem VCPUs      State Time(s)
> test                                         2 15360     1     -b---- 6617.7
> 
> But when I hotplugged the CPUs on the domU side with
> 
>   for online in /sys/devices/system/cpu/cpu*/online; do
>       echo 1 > $online
>   done
> 
> Now we see:
> 
> # xl list 2
> Name                                        ID   Mem VCPUs      State Time(s)
> test                                         2 15360     4     -b---- 6617.8
> 
> I've added this as a comment to the bugzilla.

That is a generic bug - its a race in the generic code where
the cpuX directory is created; then udev kicks off and tries to
echo 1 > cpuX/online (but online hasn't been created yet); the cpu-hotplug
code creates 'online' directory.

I've asked Greg KH about it, and here is his take:
https://lkml.org/lkml/2012/4/30/198

But I never got to prep a patch. If somebody gets to do it before me,
I owe them a beer!