Re: [RFC Patch v2 00/16] COarse-grain LOck-stepping Virtual Machines for Non-stop Service

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 11/07/13 09:35, Wen Congyang wrote:
> Virtual machine (VM) replication is a well known technique for providing
> application-agnostic software-implemented hardware fault tolerance -
> "non-stop service". Currently, remus provides this function, but it buffers
> all output packets, and the latency is unacceptable.
>
> In xen summit 2012, We introduce a new VM replication solution: colo
> (COarse-grain LOck-stepping virtual machine). The presentation is in
> the following URL:
> http://www.slideshare.net/xen_com_mgr/colo-coarsegrain-lockstepping-virtual-machines-for-nonstop-service
>
> Here is the summary of the solution:
> >From the client's point of view, as long as the client observes identical
> responses from the primary and secondary VMs, according to the service
> semantics, then the secondary VM(SVM) is a valid replica of the primary
> VM(PVM), and can successfully take over when a hardware failure of the
> PVM is detected.

How set in stone are you about the terms PVM and SVM?

SVM already has a specific meaning in Xen, being AMD Software Virtual
Machine extensions which allow for HVM guests.

As a lesser problem, PVM is sometimes used to mean PV, as a mirror of HVM.

~Andrew

>
> This patchset is RFC, and implements the frame of colo:
> 1. Both PVM and SVM are running
> 2. do checkpoint only when the output packets from PVM and SVM are different
> 3. cache write requests from SVM
>
> ChangeLog from v1 to v2:
> 1. update block-remus to support colo
> 2. split large patch to small one
> 3. fix some bugs
> 4. add a new hypercall for colo
>
> Changelog:
>   Patch 1: optimize the dirty pages transfer speed.
>   Patch 2-3: allow SVM running after checkpoint
>   Patch 4-5: modification for colo on the master side(wait a new checkpoint,
>              communicate with slaver when doing checkoint)
>   Patch 6-7: implement colo's user interface
>
>
> Wen Congyang (16):
>   xen: introduce new hypercall to reset vcpu
>   block-remus: introduce colo mode
>   block-remus: introduce a interface to allow the user specify which
>     mode the backup end uses
>   dominfo.completeRestore() will be called more than once in colo mode
>   xc_domain_restore: introduce restore_callbacks for colo
>   colo: implement restore_callbacks init()/free()
>   colo: implement restore_callbacks get_page()
>   colo: implement restore_callbacks flush_memory
>   colo: implement restore_callbacks update_p2m()
>   colo: implement restore_callbacks finish_restore()
>   xc_restore: implement for colo
>   XendCheckpoint: implement colo
>   xc_domain_save: flush cache before calling callbacks->postcopy()
>   add callback to configure network for colo
>   xc_domain_save: implement save_callbacks for colo
>   remus: implement colo mode
>
>  tools/blktap2/drivers/block-remus.c               |  188 ++++-
>  tools/libxc/Makefile                              |    8 +-
>  tools/libxc/xc_domain_restore.c                   |  264 ++++--
>  tools/libxc/xc_domain_restore_colo.c              |  939 +++++++++++++++++++++
>  tools/libxc/xc_domain_save.c                      |   23 +-
>  tools/libxc/xc_save_restore_colo.h                |   14 +
>  tools/libxc/xenguest.h                            |   51 ++
>  tools/libxl/Makefile                              |    2 +-
>  tools/python/xen/lowlevel/checkpoint/checkpoint.c |  322 +++++++-
>  tools/python/xen/lowlevel/checkpoint/checkpoint.h |    1 +
>  tools/python/xen/remus/device.py                  |    8 +
>  tools/python/xen/remus/image.py                   |    8 +-
>  tools/python/xen/remus/save.py                    |   13 +-
>  tools/python/xen/xend/XendCheckpoint.py           |  127 ++-
>  tools/python/xen/xend/XendDomainInfo.py           |   13 +-
>  tools/remus/remus                                 |   28 +-
>  tools/xcutils/Makefile                            |    4 +-
>  tools/xcutils/xc_restore.c                        |   36 +-
>  xen/arch/x86/domain.c                             |   57 ++
>  xen/arch/x86/x86_64/entry.S                       |    4 +
>  xen/include/public/xen.h                          |    1 +
>  21 files changed, 1947 insertions(+), 164 deletions(-)
>  create mode 100644 tools/libxc/xc_domain_restore_colo.c
>  create mode 100644 tools/libxc/xc_save_restore_colo.h
>