Re: making xenstore domain easy configurable

[Juergen Gross <jgross@suse.com>]

On 28/06/16 17:23, Andrew Cooper wrote:
> On 28/06/16 16:17, Doug Goldstein wrote:
>> On 6/28/16 8:59 AM, Andrew Cooper wrote:
>>> On 28/06/16 14:36, Juergen Gross wrote:
>>>> On 28/06/16 14:42, Andrew Cooper wrote:
>>>>> On 28/06/16 12:56, Juergen Gross wrote:
>>>>>> On 28/06/16 13:03, Ian Jackson wrote:
>>>>>>> Juergen Gross writes ("Re: [Xen-devel] making xenstore domain easy configurable"):
>>>>>>>> So you are telling me the xenstore domain won't work for this case?
>>>>>>> Yes.
>>>>>> That's rather unfortunate. So in order to be able to make xenstore
>>>>>> domain a common setup we need to find a solution for support of
>>>>>> xs_restrict() via xenbus, right?
>>>>>>
>>>>>> TBH, the way xs_restrict() was introduced is rather weird. It is
>>>>>> completely bound to the socket interface of oxenstored. So anyone
>>>>>> wanting to use xs_restrict() is limited to oxenstored running in
>>>>>> dom0. No way to use xenstored or a xenstore domain. I'm really
>>>>>> disappointed such a design was accepted and is now the reason for
>>>>>> not being able to disaggregate dom0.
>>>>>>
>>>>>> I've searched through the xen-devel archives and found a very
>>>>>> interesting mail:
>>>>>>
>>>>>> http://lists.xen.org/archives/html/xen-devel/2010-04/msg01318.html
>>>>>>
>>>>>> The "restrict" feature was added without any further discussion how
>>>>>> it is implemented and that the C-variant doesn't support it. The
>>>>>> explicit question about non-existing features in the C xenstored was
>>>>>> answered just with "the xenstore wire protocol doesn't change".
>>>>>>
>>>>>> With:
>>>>>>
>>>>>> http://lists.xen.org/archives/html/xen-devel/2010-07/msg00091.html
>>>>>>
>>>>>> the XS_RESTRICT value in xs_wire.h (aah, suddenly it was changed?)
>>>>>> was added. Again no mentioning of the special implementation in
>>>>>> oxenstored.
>>>>>>
>>>>>> Really, this is not how open source development should be done!
>>>>>> Maybe I'm just upset now, but I'm in favor of dropping xs_restrict()
>>>>>> support as it has been introduced in a foul way.
>>>>> I don't think the lack of xs_restrict() working over the ring should
>>>>> preclude these improvements to the configuration of how xenstored starts up.
>>>> It is limiting the solution by not allowing me to drop the sockets
>>>> completely.
>>> I don't think dropping the sockets completely is a sensible course of
>>> action.  I had come the conclusion that you were just not going to use
>>> them, as opposed to removing them entirely.
>>>
>>> For xenstored running in the same domain as the toolstack, sockets are
>>> less overhead than the shared memory ring, as no hypercalls are
>>> involved.  There is also the unfortunate problem that one of the two
>>> linux devices for xenstored *still* causes deadlocks when used; a
>>> problem which is unresolved from Linux 3.14.
>> Since Xen 4.7 the broken devices won't be used by default. I understand
>> that the socket interface is faster and less overhead but I guess my
>> question is how much data is sent over this interface? Does it really
>> matter the small performance difference to justify having two different
>> methods and not trimming the code base down to one method?
> 
> My gut feeling is that the XenServer bootstorm scalability tests will
> notice.  Our metric of "how fast is it to boot 1000 VMs" is very
> important for VDI, as employees tend to get to work and try to log
> during the same short time period.

I think I'll start with just removing the systemd socket stuff. This is
what I need to make the xenstore domain configurable on the installed
system. Removing of the sockets can be done either later or never.


Juergen


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