View source for Xen NUMA Roadmap

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= About This Page =

This page acts as a collection point for all NUMA related features. The idea is using this space to summarize the status of each of them and track their progress. This is being done with the hope of facilitating as much as possible the collaboration between the various community members, and to limit the risk of duplicating efforts.

For more general information about NUMA on Xen, check [[Xen NUMA Introduction|this page]].

== Updating this page ==

This is a Wiki, so, please, go ahead and update/fix (if not a Wiki editor, see [http://xenproject.org/component/content/article/100-misc/145-request-to-be-made-a-wiki-editor.html this]).
The maintaner of this page is [[User:Dariof|Dario]], so feel also free to contact him for anything you think you need. Even better, especially if about actual development of one of the features, start a conversation in the [http://lists.xen.org/mailman/listinfo/xen-devel xen-devel] mailing list (but in that case, be sure you follow [[Asking_Xen_Devel_Questions|this]]).

== Legend ==

In the list below, each ''Work item'' contains the name and e-mail of the person working on it. In that context, '''WORKING''' means work has already started and patches could have already been submitted or will shortly be.

'''PLANNED''', means the person is keen on doing the job, but any code have been written yet. If wanting to help or take over, consider dropping to such person a note.

If there is no name at all, the item is something identified as useful, but still unclaimed.

Finally, a '''<del>barred</del>''' work item items means it is done (and the name tells who did it).

= NUMA Features =

== Automatic VM placement ==

=== Description ===
This is about picking up a NUMA node (or a set of NUMA nodes) where a newly created VM would best execute, in order to maximize its own and the system overall performances.

Check out the [[Xen 4.2 Automatic NUMA Placement|Automatic NUMA Placement]] page.

=== Status ===
Basics are there. The old [[XEND]] toolstack had a placement logic, which did not go inot [[XL]], initially. It is now there too, starting from Xen 4.2. That being said, there is still a lot of room for improvements and making the placement algorithm more advanced and powerful.

=== Work items ===
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>): <del>at VM creation time, choose a node or a set of node where the VM fits (memory and VCPU wise) and pin the VM's VCPUs to the node's PCPUs</del>. Patch series: v1, [http://lists.xen.org/archives/html/xen-devel/2012-06/msg00978.html v2], [http://lists.xen.org/archives/html/xen-devel/2012-07/msg00231.html v3], [http://lists.xen.org/archives/html/xen-devel/2012-07/msg00475.html v4], [http://lists.xen.org/archives/html/xen-devel/2012-07/msg00682.html v5], [http://lists.xen.org/archives/html/xen-devel/2012-07/msg01017.html v6], [http://lists.xen.org/archives/html/xen-devel/2012-07/msg01256.html v7], [http://lists.xen.org/archives/html/xen-devel/2012-07/msg01493.html v8], [http://lists.xen.org/archives/html/xen-devel/2012-07/msg01514.html v9]. Relevant changesets: [http://xenbits.xen.org/hg/staging/xen-unstable.hg/rev/f4b5a21f93ad f4b5a21f93ad], [http://xenbits.xen.org/hg/staging/xen-unstable.hg/rev/4165d71479f9 4165d71479f9].
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>), WORKING: ''allow the user to control the placement algorithm by specifying some of the parameters it uses, instead of always detemining them implicitly''. Patch series: [http://lists.xen.org/archives/html/xen-devel/2012-10/msg01243.html v1], [http://lists.xen.org/archives/html/xen-devel/2012-10/msg01586.html v2] needs reposting.
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>), WORKING: ''enhance the placement algorithm to take latencies between nodes (node distances) into account''. Patch series: [http://lists.xen.org/archives/html/xen-devel/2012-10/msg01243.html v1], [http://lists.xen.org/archives/html/xen-devel/2012-10/msg01586.html v2], but too much computational complexity was being introduced, needs rethinking.
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>), PLANNED: ''provide aids to enable easy verification and testing of the placement (stressing it by generating synthetic placement request). Discussion: [http://lists.xen.org/archives/html/xen-devel/2012-07/msg00904.html 1].
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>), PLANNED: ''enhance the placement algorithm to take some more sophisticated measure of ''NODE load'' into account''.
* ''(Semi-)Automatic placement for Dom0''. Discussion: [http://lists.xen.org/archives/html/xen-devel/2012-08/msg00345.html 1].

== NUMA aware scheduling ==

=== Description ===
Instead of having to statically pin the vCPUs on nodes' pCPUs and just have them '''prefer''' running on the nodes where their memory resides. If considered independently from NUMA, this feature can be seen as giving vCPUs a sort of ''soft affinity'' (i.e., a set of pCPUs where they will prefer to run), in addition to their ''hard affinity'' (i.e., pinning).

Check out the [[Xen_4.3_NUMA_Aware_Scheduling|NUMA Aware Scheduling]] page.

=== Status ===
For credit1, it's done (see below for patches and changesets). We are now concentrating on making node affinity (soft affinity) per-vCPU, instead than per-domain. That work, still concentrating on credit1, was almost ready for going in Xen 4.4, but, because of some last minut issues, then we decided it could wait for 4.5.

For credit2, some work started, although it's quite complicated, as credit2 lacks pinning (hard affinity) too.

=== Work items ===
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>), <del>NUMA aware scheduling for credit</del>. Some related discussion (and patches): [http://lists.xen.org/archives/html/xen-devel/2012-10/msg01732.html 1]. Patch series: [http://lists.xen.org/archives/html/xen-devel/2012-10/msg00569.html v1], [http://lists.xen.org/archives/html/xen-devel/2012-12/msg01555.html v2], [http://lists.xen.org/archives/html/xen-devel/2013-02/msg00009.html v3], [http://lists.xen.org/archives/html/xen-devel/2013-03/msg01217.html v4], [http://www.gossamer-threads.com/lists/xen/devel/277277?do=post_view_threaded#277277 v5], [http://lists.xen.org/archives/html/xen-devel/2013-04/msg01568.html v6]. Relevant changesets: [http://xenbits.xen.org/hg/staging/xen-unstable.hg/rev/8bf04f2ed8de 8bf04f2ed8de], [http://xenbits.xen.org/hg/staging/xen-unstable.hg/rev/6a8c84c8e25f 6a8c84c8e25f].
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>), WORKING: ''per-vcpu soft affinity in credit''. Patch series: [http://lists.xen.org/archives/html/xen-devel/2013-10/msg00164.html v1], [http://lists.xenproject.org/archives/html/xen-devel/2013-11/msg00468.html v1-resend], [http://lists.xenproject.org/archives/html/xen-devel/2013-11/msg01953.html v2], [http://lists.xenproject.org/archives/html/xen-devel/2013-11/msg02513.html v3], [http://lists.xenproject.org/archives/html/xen-devel/2013-11/msg03364.html v4], [http://lists.xen.org/archives/html/xen-devel/2013-12/msg00257.html v5], [http://lists.xen.org/archives/html/xen-devel/2013-12/msg01155.html v5-resend]. v6 is in [http://xenbits.xen.org/gitweb/?p=people/dariof/xen.git;a=shortlog;h=refs/heads/numa/per-vcpu-affinity-v6 this git branch], waiting to be rebased and reposted as soon as Xen 4.5 development cycle opens.
* Justin ([mailto:jtweaver@hawaii.edu jtweaver@hawaii.edu]), WORKING: ''Hard and soft affinity for credit2''. Discussion: [http://lists.xen.org/archives/html/xen-devel/2013-12/msg01391.html 1]. Patch series: [http://lists.xen.org/archives/html/xen-devel/2013-12/msg02190.html v1], [http://www.gossamer-threads.com/lists/xen/devel/311062 v2]. While working on this, a bug on how credit2 handles multiple runqueues was found. Here they are the attempt to fix that, as preliminary work: [http://www.gossamer-threads.com/lists/xen/devel/316253?do=post_view_threaded v1], [http://comments.gmane.org/gmane.comp.emulators.xen.devel/187692 v2], [http://www.gossamer-threads.com/lists/xen/devel/316598?page=last v3]

== Virtual NUMA (support for NUMA guests) ==

=== Description ===
If a guest ends up on more than one nodes, make sure it knows it's running on a NUMA platform (smaller than the actual host, but still NUMA). It is something very important for some specific kind of workloads, for instance, HPC ones. In fact, it the guest OS (and application) has any NUMA support, exporting a virtual topology to the guest is the only way to render that effective, and perhaps filling at least to some extent the gap introduced by the needs of distributing the guests on more than one node. Under the name of vNUMA, this is one of the key and most advertised feature of VMWare vSphere 5 ("[http://cto.vmware.com/vnuma-what-it-is-and-why-it-matters/ vNUMA: what it is and why it matters]").

=== Status ===
For PV guests, most of the work is done (by [http://hellokernel.blogspot.it/ Elena], while participating in [https://wiki.gnome.org/OutreachProgramForWomen/2013/JuneSeptember#Linux_Kernel Round 6 of OPW]), although it still needs to be properly upstreamed. Various patch series have been submitted along such period, here's the most relevant ones: first RFC [http://lists.xen.org/archives/html/xen-devel/2013-08/msg02533.html for Xen], [http://lists.xen.org/archives/html/xen-devel/2013-08/msg02555.html for Linux]; second RFC [http://lists.xen.org/archives/html/xen-devel/2013-09/msg01337.html for Xen], [http://lists.xen.org/archives/html/xen-devel/2013-09/msg01721.html for Linux]; actual v1 [http://lists.xen.org/archives/html/xen-devel/2013-10/msg01376.html for Xen]; v2 [http://lists.xenproject.org/archives/html/xen-devel/2013-11/msg01999.html for Xen], [http://lists.xenproject.org/archives/html/xen-devel/2013-11/msg02565.html for Linux]; v3 [http://osdir.com/ml/general/2013-11/msg30648.html for Xen]; v4 [http://lists.xen.org/archives/html/xen-devel/2013-12/msg00625.html for Xen].

Having vNUMA in both Dom0 and DomU will enable some potentially relevant optimizations, e.g., wrt the split driver model Xen supports, making sure to run the backend and the frontend on the same NUMA  node, and/or to run the backend on the same node where the IO device is also attached (see also IONUMA below). Some thoughts about this [http://www.gossamer-threads.com/lists/xen/devel/283037?do=post_view_threaded here].

=== Work Items ===
* Elena (<[mailto:ufimtseva@gmail.com ufimtseva@gmail.com]>), WORKING: ''upstream PV vNUMA in both Xen and Linux''.
* Matt (<[mailto:msw@linux.com msw@linux.com]>), ''send in an RFC''.
* automatic placement for resuming/migrating domains: if they have a virtual topology, better not to change it;
* memory migration: it can change the actual topology (should we update it on-line or disable memory migration?)

== Dynamic memory migration ==

=== Description ===
Between different nodes of one host, either upon user request or automatically, as a form of load balancing (similar to what happens on the CPU with the NUMA-aware scheduler. Some development for this features happened during the Xen 4.3 window, but then got stalled. It is supposed to start back during the 4.5 development window.

=== Status ===
Started, but not yet ready to leave some developer's private patch queue in their dev-boxes. The need to support both HVM and PV guests complicate things quite a bit. Xenbus, qemu, a lot of inherent characteristics of the Xen architecture get in the way of having it simply done within the hypervisor (as it happens for NUMA aware scheduling). The current idea being pursued is for it to happen at low toolstack level (perhaps with the hypervisor exporting statistics that will help toolstacks and users to undertake proper decisions), sort-of mimicking a suspend-resume cycle.

=== Work item ===
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>), WORKING: ''enable moving memory from one node to another (on the same host)''.
* [[User:Dariof|Dario]] (<[mailto:dario.faggioli@citrix.com dario.faggioli@citrix.com]>), PLANNED: ''track how many and from whom non node-local memory is being accessed''.

==  IONUMA support ==

=== Description ===
If not only memory, but also I/O controllers are attached to specific nodes, you'll end up with devices which are better used by VMs running on those nodes (or vice-versa, VMs that are better run on the proper node if/when they want to use a specific device).

=== Status ===
Yang Zhang did some previous investigation on this situation, which , BTW, goes under the name IONUMA, and the result is this presentation [http://xen.org/files/xensummit_seoul11/nov2/5_XSAsia11_KTian_IO_Scalability_in_Xen.pdf I/O Scalability in Xen] at Xen Summit 2011.

Apart from that, only some discussion happened, on xen-devel: [http://lists.xen.org/archives/html/xen-devel/2012-08/msg00161.html 1], [http://lists.xen.org/archives/html/xen-devel/2012-06/msg01683.html 2], [http://lists.xen.org/archives/html/xen-devel/2013-05/msg01984.html 3].

Some more discussion, related to this, happened recently in these two threads: [http://lists.xen.org/archives/html/xen-devel/2014-02/msg01154.html 1] (about PCIe proximity domains), [http://lists.xen.org/archives/html/xen-devel/2014-01/msg00098.html 2] (about introducing some [http://www.open-mpi.org/projects/hwloc/ hwloc] support for a Xen host).

=== Work item ===
* ''export IONUMA information to the user'', as we currently do for NUMA topology with, in that case, <code>xl info -n</code>;
* ''IONUMA and automatic placement'': as said in the description, IONUMA info (once available) should bias the automatic placement decisions;
* ''Dom0/Driver IONUMA'': devices should have their DMA buffers for the backends allocated on (or as close as possible to) the node where their IO controller is attached;
* ''guest IONUMA'': devices passed-through to guests, should have their DMA buffers allocated on (or as close as possible to) the node where their IO controller is attached.

[[Category:Performance]]
[[Category:Xen]]
[[Category:Developers]]
[[Category:NUMA]]
[[Category:Transient]]
[[Category:Roadmap]]
[[Category:Xen 4.2]]
[[Category:Xen 4.3]]
[[Category:Xen 4.4]]
[[Category:Resource Management]]