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Re: [MirageOS-devel] xen dev summit talk slides: Branch Consistency for Xenstore

Hi Anil, all,

As a clarification, the talk was given by my colleague Filipe Manco, in
cc, not me. Iâve temporarily placed the slides at:


They should appear on the Xen summit briefly, and more permanently on our
website at:



â Felipe

Dr. Felipe Huici
Senior Researcher, Networked Systems and Data
Analytics Group
NEC Laboratories Europe, Network Research Division
Kurfuerstenanlage 36, D-69115 Heidelberg
Tel.     +49
(0)6221 4342-241
Fax:     +49
(0)6221 4342-155

NEC Europe Limited Registered Office: NEC House, 1
Victoria Road, London W3 6BL Registered in England 2832014

On 8/19/14, 3:47 PM, "Anil Madhavapeddy" <anil@xxxxxxxxxx> wrote:

>On 19 Aug 2014, at 08:44, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
>> On 17 Aug 2014, at 11:01, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
>>> I'm giving a talk at the Xen Developer Summit at Linuxcon tomorrow on
>>>the work that we've (primarily Dave Scott and Thomas Gazagnaire) on
>>>improving the Xenstore via Irmin features.
>>> Slides here: http://decks.openmirage.org/xendevsummit14#/
>>> Repo: https://github.com/mirage/mirage-decks as usual
>> [+xen-api-devel] Talk went well, quick notes here:
>> - git workflow very popular. Lots of people twigged onto the
>>maintainability benefits of `git bisect` automation in particular.
>> - questions about why Xenstore transactions are still necessary in the
>>modern world.  Can replace with consensus protocols instead?  Maybe time
>>for an ABI bump to deprecate the ancient xenstore protocol.
>> - space usage is a concern -- building an RRD-style constant size
>>library to maintain progressive history would be a big win.
>> - *excellent* talk from Felipe Huici (CCed) from NEC about building
>>much denser VM workloads, and he observed that Xenstored/xenconsoled are
>>a big bottleneck at ~10000 VMs.  Are your slides available Felipe?  Some
>>sub notes:
>> - we could write a mirage xenconsoled to log to irmin and drain guest
>>console rings much faster.
>> - a distributed xenstored+irmin would allow significantly more
>>scalability than attempting to build a serially fast version.
>> - felipe has the beginning of a simple c++ xenstored that doesn't
>>implement the full semantics, but is enough for MiniOS.
>> - it may be useful to negotiate a xenstore v2 protocol and use that for
>>new guests.  It could use a simple fixed-length binary protocol
>>(protobuf-style?), and eliminate the need for transactions perhaps.
>sent 'send' too quickly.  The most important point:
>- xenstore need consistent indices.  Using domain names in the current
>stack results in a linear search through all domids -- very slow with
>10000 VMs!  Irmin could maintain a branch that updates a 'name -> domid'
>that is consistent within the transaction, and do constant time lookups
>for the toolstack.

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