Documentation and guides

Weekly Meeting: 2014-08-20

20th Aug 2014: XenSummit feedback, Conduit patches and ARM profiling

Agenda

Attendees: Amir Chaudhry (chair), Thomas Gazagnaire, Thomas Leonard, Jon Ludlam, Anil Madhavapeddy, Richard Mortier and Dave Scott.

Notes

XenSummit Talk

Anil is in Chicago at the annual Xen Developer Summit speaking about Mirage 2.0 and branch consistency for Xen Stub Domains (abstract). Some feedback from the talk was emailed to the list and is summarised here (see the thread for discussion).

In general, it was very positive and there was lots of interest in Irmin. Some feedback from attendees is that some more structure around Mirage would help people who want to contribute. Right now there are libraries everywhere and it's difficult to see where you can get involved without having to understand everything. Making a framework around the upcoming headline features would be especially useful. This would be something like a roadmap for Mirage 3.0. Overall, we should be aiming to get better at this kind of thing with every release (and for the most part, we seem to be — feedback is always welcome!).

Conduit merge

Got HTTP request working through Mirage. Requires DNS and TCP set up and the like. It's quite a big patch set, which touches a number of libraries and a number of things are not backward compatible. Hence these need to be co-ordinated and there's an issue to track this (mirage/mirage#287). Dave will add vchan support when ready. This is an important set of patches and we will get a working transport layer. The updates to mirage-skeleton are minor and also tracked in the issue.

Irmin status update

ThomasG investigating how he could remove the core_kernel dependency and is also cleaning up Benjamin Farinier's queues and ropes work to port that in. Bug reports are coming in from early users and one of the main points is that we should improve the user side of things.

Profiling ARM

ThomasL trying to get profiling data out of ARM, with the intent of producing some fun and useful graphs to share.

Anil previously mentioned getting ethernet at 100MB. Seems we can get 18MB over UDP at the moment and Linux only manages 13MB. TCP on Mirage is 11MB and Linux gets 40MB. Not really clear what these difference are due to. Also tried to dump from console but turned out to be Xen that was rate limiting things. Anil suggested that Thomas check that the free slots in rings are being fully utilised.

It would be really useful if opam can make the profiling process easier. A compiler switch could help with this and ThomasG can look into that (for native, not bytecode).

When this is done, ThomasL will write it all up with lots of pretty graphs.

Xen-ARM vs Xen-x86

Amir has some fairly basic questions about Xen, Mirage and ARM. Specifically, what the differences are between Xen on the cloud (x86) and embedded devices (ARM). Others tell him this mainly relates to Mini-OS and it's relation to Mirage (and ClickOS and HaLVM etc). There are several posts that might help explain things, for example ThomasL's blog post on ARM and wiki pages on Xen events and setting up a Cubieboard2. Amir will start with those and if anything isn't clear, he'll ask ThomasG about it. Amir might write this up for the website if it'll help explain to others too.

[edit: This is proof that there's no such thing as a stupid question - AC]

AoB