Archived/Xen Development Projects

This page lists various Xen related development projects that can be picked up by anyone! If you're interesting in hacking Xen this is the place to start! Ready for the challenge?

To work on a project:

• Find a project that looks interesting (or a bug if you want to start with something simple)
• Send an email to xen-devel mailinglist and let us know you started working on a specific project.
• Post your ideas, questions, RFCs to xen-devel sooner than later so you can get comments and feedback.
• Send patches to xen-devel early for review so you can get feedback and be sure you're going into correct direction.
• Your work should be based on xen-unstable development tree, if it's Xen and/or tools related. After your patch has been merged to xen-unstable it can be backported to stable branches (Xen 4.0, Xen 3.4, etc).
• Your kernel related patches should be based on either upstream kernel.org git tree (latest version), or xen/stable-2.6.32.x tree, depending if it's upstream or xen dom0 related work.

xen-devel mailinglist subscription and archives: http://lists.xensource.com/mailman/listinfo/xen-devel

Before to submit patches, please look at Submitting Xen Patches wiki page.

If you have new ideas, suggestions or development plans let us know and we'll update this list!

List of projects

Domain support

Upstreaming Xen PVSCSI drivers to mainline Linux kernel Date of insert: 01/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: PVSCSI drivers needs to be upstreamed yet. Necessary operations may include: Task 1: Upstream PVSCSI scsifront frontend driver (for domU). Task 2: Upstream PVSCSI scsiback backend driver (for dom0). Send to various related upstream mailinglists for review, comments. Fix any upcoming issues. Repeat until merged to upstream Linux kernel git tree. http://git.kernel.org/?p=linux/kernel/git/konrad/xen.git;a=shortlog;h=refs/heads/devel/xen-scsi.v1.0 More info: http://wiki.xen.org/xenwiki/XenPVSCSI Outcomes: Not specified, project outcomes

Upstreaming Xen PVUSB drivers to mainline Linux kernel Date of insert: 01/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: PVUSB drivers needs to be upstreamed yet. Necessary operations may include: Upstream PVUSB usbfront frontend driver (for domU). Upstream PVUSB usbback backend driver (for dom0). Send to various related upstream mailinglists for review, comments. Fix any upcoming issues. Repeat until merged to upstream Linux kernel git tree. http://git.kernel.org/?p=linux/kernel/git/konrad/xen.git;a=shortlog;h=refs/heads/devel/xen-usb.v1.1 More info: http://wiki.xen.org/xenwiki/XenUSBPassthrough Outcomes: Not specified, project outcomes

Blkback improvements Date of insert: 02/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: Blkback requires a number of improvements, some of them being: Multiple disks in a guest cause contention in the global pool of pages. There is only one ring page and with SSDs nowadays we should make this larger, implementing some multi-page support. With multi-page it becomes apparent that the segment size ends up wasting a bit of space on the ring. BSD folks fixed that by negotiating a new parameter to utilize the full size of the ring. Add DIF/DIX support [1] Further perf evaluation needs to be done to see how it behaves under high load. Outcomes: Not specified, project outcomes

Netback overhaul Date of insert: 02/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: Wei Liu posted RFC patches that make the driver be multi-page, multi-event channel and with a page-pool. However not all the issues have been addressed yet, meaning that the patches need to be finished and cleaned up yet. Additively, a zero-copy implementation can be considered. Patch serie and discussions: http://lists.xen.org/archives/html/xen-devel/2012-01/msg02561.html http://www.spinics.net/lists/linux-nfs/msg22575.html Outcomes: Not specified, project outcomes

PAT writecombine fixup Date of insert: 02/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: The writecombine feature (especially for graphic adapters) is turned off due to stability reasons. More specifically, the code involved in page transition from WC to WB gets confused about the PSE bit state in the page, resulting in a set of repeated warnings. For more informations please check: Linux git revision 8eaffa67b43e99ae581622c5133e20b0f48bcef1 http://lists.xen.org/archives/html/xen-devel/2012-06/msg01950.html Outcomes: Not specified, project outcomes

ACPI S3-state investigation and fixup Date of insert: 02/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: During Linux-3.3 release the the S3-state was supposed to work including these patches: https://git.kernel.org/?p=linux/kernel/git/konrad/xen.git;a=shortlog;h=refs/heads/devel/acpi-s3.v9 But now it is not working anymore. Scope of the project is understanding the reasons for the issues and fix them. Outcomes: Not specified, project outcomes

Parallel xenwatch Date of insert: 01/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: Xenwatch is locked with a coarse lock. For a huge number of guests this represents a scalability issue. The need is to rewrite the xenwatch locking in order to support full scalability. Outcomes: Not specified, project outcomes

Hypervisor

Microcode uploader implementation Date of insert: 02/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: Intel is working on early implementation where the microcode blob would be appended to the initrd image. The kernel would scan for the appropiate magic constant and load the microcode very early. The Xen hypervisor can do this similary. Outcomes: Not specified, project outcomes

SEDF Handling of Blocking/Unblocking Date of insert: 08/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Dario Faggioli <dario.faggioli@citrix.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: The SEDF scheduler, within Xen, currently deals with events such as a vcpu blocking (in general, stopping running) and unblocking (in general, restarting running) by trying (but failing!) to special case all the possible situations, resulting in the code being rather complicated, ugly, inefficient and hard to maintain. Unified approaches have been proposed for enabling blocking and unblocking in EDF (the algorithm the scheduler uses), without compromising the temporal isolation it provides to the various tasks/vcpus. More specifically, the technique called Constant BandWidth Server (CBS) could easily be implemented. Outcomes: Not specified, project outcomes

SEDF Multiprocessor Support Date of insert: 08/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Dario Faggioli <dario.faggioli@citrix.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: The SEDF scheduler, within Xen, does not properly handle SMP systems, unless specific vcpu pinning is specified by the user. That is a big limitation of the current implementation, especially since EDF (the algorithm the scheduler uses) could be easily extended to work in that situations. The first thing to do would be turn from using one SEDF runqueue per processor one runqueue per "cluster of processors" (like for instance using one runqueue per-L3, as scredit2 is doing). That would already increase the effectiveness of the scheduler on current hardware a lot. After that, a mechanism for balancing and migrating vcpus among different runqueues can be designed and implemented. Outcomes: Not specified, project outcomes

Integrating NUMA and Tmem Date of insert: 08/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Dario Faggioli <dario.faggioli@citrix.com>, Dan Magenheimer <dan.magenheimer_AT_oracle_DOT_com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: Trascendent memory (Tmem) as a mechanism for discriminating between frequently and infrequently used data, and thus helping allocating them properly. It would be interesting to investigate and implement all the necessary mechanisms to take advantage of this and improve performances of Tmem enabled guests running on NUMA machines. Some more details here. Outcomes: Not specified, project outcomes

Userspace Tools

Convert PyGrub to C Date of insert: 15/11/2012; Verified: Not updated in 2020; GSoC: Yes Technical contact: Roger Pau Monné <roger.pau@citrix.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: With the replacement of xend with xl/libxl, PyGrub is the only remaining Python userspace component of the Xen tools. Since it already depends on a C library (libfsimage), converting it to C code should not be a huge effort. PyGrub Python code is no more than a parser to grub and syslinux configuration files. Some embedded distros (mainly Alpine Linux) already mentioned it's interest in dropping the Python package as a requirement for a Dom0, this will make a Xen Dom0 much more smaller. Outcomes: Not specified, project outcomes

Refactor Linux hotplug scripts Date of insert: 15/11/2012; Verified: Not updated in 2020; GSoC: Yes Technical contact: Roger Pau Monné <roger.pau@citrix.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: Current Linux hotplug scripts are all entangled, which makes them really difficult to understand or modify. The reason of hotplug scripts is to give end-users the chance to "easily" support different configuration for Xen devices. Linux hotplug scripts should be analized, providing a good description of what each hotplug script is doing. After this, scripts should be cleaned, putting common pieces of code in shared files across all scripts. A Coding style should be applied to all of them when the refactoring is finished. Outcomes: Not specified, project outcomes

Performance

Performance tools overhaul Date of insert: 02/08/2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: Generally, works on the performance tool themselves should be listes separately to the Xen_Profiling:_oprofile_and_perf wiki page. Outcomes: Not specified, project outcomes

Upstream bugs!

VCPU hotplug bug Date of insert: Sep 1 2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: VCPU hotplug. [2] To get this its as easy as having this in your guest config: vcpus=2 maxvcpus=3 And when you launch the guest to play with 'xm vcpu-set 0 2', xm vcpu-set 0 3' and see the guest forget about one of the CPUs. This is what you will see in the guest: udevd-work[2421]: error opening ATTR{/sys/devices/system/cpu/cpu2/online} for writing: No such file or directory If you instrument udev and look at the code you will find somebody came up with a "fix": http://serverfault.com/questions/329329/pv-ops-kernel-ignoring-cpu-hotplug-under-xen-4-domu But the real fix is what Greg outlines in the URL above. Outcomes: Not specified, project outcomes

RCU timer sent to offline VCPU Date of insert: Sep 1 2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: [ 0.073006] WARNING: at /home/konrad/ssd/linux/kernel/rcutree.c:1547 __rcu_process_callbacks+0x42e/0x440() [ 0.073008] Modules linked in: [ 0.073010] Pid: 12, comm: migration/2 Not tainted 3.5.0-rc2 #2 [ 0.073011] Call Trace: [ 0.073017] <IRQ> [<ffffffff810718ea>] warn_slowpath_common+0x7a/0xb0 which I get with this guest config: vcpus=2 maxvcpus=3 Here is what Paul says: https://lkml.org/lkml/2012/6/19/360 Outcomes: Not specified, project outcomes

CONFIG_NUMA on 32-bit. Date of insert: Sep 1 2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: http://www.spinics.net/lists/kernel/msg1350338.html I came up with a patch for the problem that William found: http://lists.xen.org/archives/html/xen-devel/2012-05/msg01963.html and narrowed it down the Linux calling xen_set_pte with a PMD flag (so trying to setup a 2MB page). Currently the implemenation of xen_set_pte can't do 2MB but it will gladly accept the argument and the multicall will fail. Peter did not like the x86 implemenation so I was thinking to implement some code in xen_set_pte that will detect that its a PMD flag and do "something". That something could be either probe the PTE's and see if there is enough space and if so just call the multicall 512 times, or perform a hypercall to setup a super-page. .. But then I wasn't sure how we would tear down such super-page. Outcomes: Not specified, project outcomes

Time accounting for stolen ticks. Date of insert: Sep 1 2012; Verified: Not updated in 2020; GSoC: Unknown Technical contact: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Mailing list/forum for project: xen-devel@ IRC channel for project: #xen-devel Difficulty: Unknown Skills Needed: Unknown Description: This is http://git.kernel.org/?p=linux/kernel/git/konrad/xen.git;a=shortlog;h=refs/heads/devel/pvtime.v1.1 and whether those patches are the right way or the bad way. The discussion of this is at http://lists.xen.org/archives/html/xen-devel/2011-10/msg01477.html Outcomes: Not specified, project outcomes

Xen Cloud Platform (XCP) and XAPI projects

There are separate wiki pages about XCP and XAPI related projects. Make sure you check these out aswell!

• XCP and XAPI development projects: XAPI project suggestions
• XCP short-term roadmap: XCP short term roadmap
• XCP monthly developer meetings: XCP Monthly Meetings
• XAPI developer guide: XAPI Developer Guide

Quick links to changelogs of the various Xen related repositories/trees

Please see XenRepositories wiki page!