Xen devel - Jul 2005 - [PATCH] enforce dom0 cpus and balloon out memory

This patch does 2 jobs:

- Enforce the number of CPUs dom0 will take. See the new variable
"dom0-cpus" in xend-config.sxp (you will want to set this variable to
1 on SMP systems)

- Balloon out dom0 memory when creating domU, if there is not enough
free memory. The lowest level we will balloon out is configured via
the new variable "dom0-min-mem" in xend-config.sxp


I still have a doubt: where to put the code to enforce dom0-cpus. At
the moment I put it into
python/xen/xend/server/SrvDaemon.py, and hopefully that is resonable
enough. Any comment?



Signed-off-by: Nguyen Anh Quynh <aquynh@gmail.com>



$ diffstat enforce_resource.patch 
 examples/xend-config.sxp            |    8 +++++++
 python/xen/xend/XendRoot.py         |   10 +++++++++
 python/xen/xend/server/SrvDaemon.py |   30 +++++++++++++++++++++++++++-
 python/xen/xm/create.py             |   38 ++++++++++++++++++++++++++++++++++++
 4 files changed, 85 insertions(+), 1 deletion(-)


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* aq <aquynh@gmail.com> [2005-07-29 09:01]:
> This patch does 2 jobs:
> 
> - Enforce the number of CPUs dom0 will take. See the new variable
> "dom0-cpus" in xend-config.sxp (you will want to set this
variable to
> 1 on SMP systems)
You could use vcpu-hotplug to drop the extra cpus from dom0 instead of
writing directly into sysfs.  The only stopper to that approach is the
fact that dom0''s self.channel is not initialized when xend starts and
subsequently doesn''t send the control message.  Channels are
initialized
when a domain is built, but since dom0 is built by xen, the routine
which sets up channels isn''t called for dom0.  Haven''t found a
good place
for xend to initialized the channel for dom0 yet either.

See vcpu_hotplug() in xen/xend/XendDomInfo.py

Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com

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> You could use vcpu-hotplug to drop the extra cpus from dom0 instead of
> writing directly into sysfs.  The only stopper to that approach is the
> fact that dom0''s self.channel is not initialized when xend starts
and
> subsequently doesn''t send the control message.  Channels are
initialized
> when a domain is built, but since dom0 is built by xen, the routine
> which sets up channels isn''t called for dom0.  Haven''t
found a good place
> for xend to initialized the channel for dom0 yet either.
Hmmm.  Is the channel never set up then?  It''d certainly be nice if it
were:
then you can use "xm balloon" to set dom0''s memory footprint,
which is
preferable to using the /proc interface directly.

Cheers,
Mark
>
> See vcpu_hotplug() in xen/xend/XendDomInfo.py
>
> Ryan Harper
> Software Engineer; Linux Technology Center
> IBM Corp., Austin, Tx
> (512) 838-9253   T/L: 678-9253
> ryanh@us.ibm.com
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
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* Mark Williamson <mark.williamson@cl.cam.ac.uk> [2005-07-29
10:25]:
> > You could use vcpu-hotplug to drop the extra cpus from dom0 instead of
> > writing directly into sysfs.  The only stopper to that approach is the
> > fact that dom0''s self.channel is not initialized when xend
starts and
> > subsequently doesn''t send the control message.  Channels are
initialized
> > when a domain is built, but since dom0 is built by xen, the routine
> > which sets up channels isn''t called for dom0. 
Haven''t found a good place
> > for xend to initialized the channel for dom0 yet either.
> 
> Hmmm.  Is the channel never set up then?  It''d certainly be nice
if it were:
Correct.  As mentioned above, this is only a problem for dom0 since the
xend contruct_image() code isn''t called for dom0 as xen is the builder.
The fix is as simple as calling create_channel() from dom0''s
XendDomInfo
object.  I''ve not determined the appropriate location to issue the
call.
> then you can use "xm balloon" to set dom0''s memory
footprint, which is
> preferable to using the /proc interface directly.
Indeed.  Same goes for using vcpu_hotplug() versus sysfs

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com

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> You could use vcpu-hotplug to drop the extra cpus from dom0 
> instead of writing directly into sysfs.  The only stopper to 
> that approach is the fact that dom0''s self.channel is not 
> initialized when xend starts and subsequently doesn''t send 
> the control message.  Channels are initialized when a domain 
> is built, but since dom0 is built by xen, the routine which 
> sets up channels isn''t called for dom0.  Haven''t found a
good
> place for xend to initialized the channel for dom0 yet either.
> 
> See vcpu_hotplug() in xen/xend/XendDomInfo.py
Yep, I''d much prefer this approach -- its annoying the tools
don''t work
on dom0. Volunteers?

Ian

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On 29 Jul 2005, at 18:26, Ian Pratt wrote:
>>
>> See vcpu_hotplug() in xen/xend/XendDomInfo.py
>
> Yep, I''d much prefer this approach -- its annoying the tools
don''t work
> on dom0. Volunteers?
They certainly *ought* to work. I can assure you that xend does connect 
to domain0''s control interface. Otherwise you could not set up virtual 
blkif and netif connections to backend drivers running in domain0!

This should be a small bugfix: no major implementation effort required. 
:-)

  -- Keir


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* Keir Fraser <Keir.Fraser@cl.cam.ac.uk> [2005-07-29
13:20]:
> 
> On 29 Jul 2005, at 18:26, Ian Pratt wrote:
> 
> >>
> >>See vcpu_hotplug() in xen/xend/XendDomInfo.py
> >
> >Yep, I''d much prefer this approach -- its annoying the tools
don''t work
> >on dom0. Volunteers?
> 
> They certainly *ought* to work. I can assure you that xend does connect 
> to domain0''s control interface. Otherwise you could not set up
virtual
> blkif and netif connections to backend drivers running in domain0!
> 
> This should be a small bugfix: no major implementation effort required. 
> :-)
Agreed.  It is a simple matter of find the right place in the xend code
to initialize the self.channel (calling crate_channel()) for dom0.

I reported this a while ago.  _something_ is wrong with self.channel in
XendDomInfo object for dom0 as I noted in this message:

http://lists.xensource.com/archives/html/xen-devel/2005-07/msg00444.html

Also in bugzilla #101, I added a patch to show that the control message
wasn''t sent because the channel is not valid.

http://bugzilla.xensource.com/cgi-bin/bugzilla/show_bug.cgi?id=101


-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh@us.ibm.com

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