Re: Xen 4.2 Release Plan / TODO

[George Dunlap <George.Dunlap@eu.citrix.com>]

On Tue, Apr 10, 2012 at 11:24 AM, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> Plan for a 4.2 release:
> http://lists.xen.org/archives/html/xen-devel/2012-03/msg00793.html
>
> The time line is as follows:
>
> 19 March        -- TODO list locked down
> 2 April         -- Feature Freeze
>                                                       << WE ARE HERE
> Mid/Late April  -- First release candidate
> Weekly          -- RCN+1 until it is ready
>
> The updated TODO list follows. Per the release plan a strong case will
> now have to be made as to why new items should be added to the list,
> especially as a blocker, rather than deferred to 4.3.
>
> We have now entered Feature Freeze. Patches which have been posted
> before or which address something on the list below are still acceptable
> (for now, we will gradually be getting stricter about this), everything
> else will be deferred until 4.3 by default.
>
> Lots more DONE this week, still a few big ticket items or items with no
> progress (that I've noticed) please let me know if the status of
> anything has changed.
>
> From next week I think I will start also tracking bugs on these lists.
> Please let me know if you have something which you feel should be listed
> here, as well as your justification for it being a blocker rather than
> "nice to fix".

Here are bugs I've found:

* Zombie driver domains.  There's a bug where PV guests with devices
passed through with xl hang around as "zombies", with one outstanding
page reference.  I think this should really be a blocker.  I'm working
on this at the moment.

* Manually ballooning dom0.  xl mem-set 0 [foo] fails with "libxl:
error: libxl.c:2569:libxl_set_memory_target: cannot get memory info
from /local/domain/0/memory/static-max: No such file or directory".
I'd make this a blocker just because it should be easy to fix and it's
pretty embarassing.  This might be suitable for an enthusiastic
on-looker.

Also, since there have been other situations / reports of zombie
domains, it would be good if we could get a zombie domain detector
into the testing system to see how widespread they are.

 -George

>
> hypervisor, blockers:
>      * NONE?
>
> tools, blockers:
>      * libxl stable API -- we would like 4.2 to define a stable API
>        which downstream's can start to rely on not changing. Aspects of
>        this are:
>              * Safe fork vs. fd handling hooks. Involves API changes
>                (Ian J, patches posted)
>              * locking/serialization, e.g., for domain creation. As of
>                now,  nothing is provided for this purpose, and
>                downstream toolstacks have to put their own mechanisms
>                in place. E.g., xl uses a fcntl() lock around the whole
>                process of domain creation. It should OTOH be libxl job
>                to offer a proper set of hooks --placed at the proper
>                spots during the domain creation process-- for the
>                downstreams to fill with the proper callbacks. (Dario
>                Faggioli)
>                      * Thinking to defer this until 4.3?
>              * agree & document compatibility guarantees + associated
>                technical measures (Ian C, DONE)
>      * xl compatibility with xm:
>              * feature parity wrt driver domain support (George Dunlap,
>                DONE)
>              * xl support for "rtc_timeoffset" and "localtime" (Lin
>                Ming, DONE)
>      * More formally deprecate xm/xend. Manpage patches already in
>        tree. Needs release noting and communication around -rc1 to
>        remind people to test xl.
>      * Domain 0 block attach & general hotplug when using qdisk backend
>        (need to start qemu as necessary etc) (Stefano S, patches
>        posted)
>      * file:// backend performance. qemu-xen-tradition's qdisk is quite
>        slow & blktap2 not available in upstream kernels. Need to
>        consider our options:
>              * qemu-xen's qdisk is thought to be well performing but
>                qemu-xen is not yet the default. Complexity arising from
>                splitting qemu-for-qdisk out from qemu-for-dm and
>                running N qemu's.
>              * potentially fully userspace blktap could be ready for
>                4.2 (unlikely to be available in 4.2)
>              * use /dev/loop+blkback. This requires loop driver AIO and
>                O_DIRECT patches which are not (AFAIK) yet upstream.
>              * Leverage XCP's blktap2 DKMS work. (Useful fallback for
>                some usecases
>        Stefano has done a lot of work here and has proposed some
>        performance improvements for qdisk in both qemu-xen and
>        qemu-xen-traditional which make them a plausible alternative for
>        Xen 4.2. This is likely the route we will now take. Need to
>        mention in release notes?
>      * Improved Hotplug script support (Roger Pau Monné, patches
>        posted)
>      * Block script support -- follows on from hotplug script (Roger
>        Pau Monné)
>
> hypervisor, nice to have:
>      * solid implementation of sharing/paging/mem-events (using work
>        queues) (Tim Deegan, Olaf Herring et al -- patches posted)
>              * "The last patch to use a waitqueue in
>                __get_gfn_type_access() from Tim works.  However, there
>                are a few users who call __get_gfn_type_access with the
>                domain_lock held. This part needs to be addressed in
>                some way."
>      * Sharing support for AMD (Tim, Andres).
>      * PoD performance improvements (George Dunlap)
>
> tools, nice to have:
>      * Configure/control paging via xl/libxl (Olaf Herring, lots of
>        discussion around interface, general consensus reached on what
>        it should look like. Olaf has let me know that he is probably
>        not going to have time to do this for 4.2, will likely slip to
>        4.3 unless someone else want to pick up that work)
>      * Upstream qemu feature patches:
>              * Upstream qemu PCI passthrough support (Anthony Perard,
>                patches sent)
>              * Upstream qemu save restore (Anthony Perard, Stefano
>                Stabellini, qemu patches applied, waiting for libxl etc
>                side which has been recently reposted)
>      * Nested-virtualisation. Currently "experimental". Likely to
>        release that way.
>              * Nested SVM. Tested in a variety of configurations but
>                still some issues with the most important use case (w7
>                XP mode) [0]  (Christoph Egger)
>              * Nested VMX. Needs nested EPT to be genuinely useful.
>                Need more data on testedness etc (Intel)
>      * Initial xl support for Remus (memory checkpoint, blackholing)
>        (Shriram, patches reposted recently, was blocked behind qemu
>        save restore patches which are now in)
>      * xl compatibility with xm:
>              * xl support for autospawning vncviewer (vncviewer=1 or
>                otherwise) (Goncalo Gomes, patches posted)
>              * support for vif "rate" parameter (Mathieu Gagné, patches
>                posted)
>              * expose PCI back "permissive" parameter (George Dunlap)
>
> [0] http://lists.xen.org/archives/html/xen-devel/2012-03/msg00883.html
>
>
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