Re: [Qemu-devel] [PATCH v3 00/35] postcopy live migration

[Orit Wasserman]

Hi,
I didn't have time yet to review in detail your patches,
but I have one general comment about the interface to activate postcopy.
As postcopy needs to be supported both by source and destination Qemu,
for those kind of features we have migration capabilities interface,
you can look at the XBZRLE patch series for more details.
So in order to activate postcopy the user will need to do:
"migrate_set_capabilites postcopy on" on source and destination Qemu before 
starting
the migration process.

Regards,
Orit 

On 10/30/2012 10:32 AM, Isaku Yamahata wrote:
> This is the v3 patch series of postcopy migration.
> 
> The trees is available at
> git://github.com/yamahata/qemu.git qemu-postcopy-oct-30-2012
> git://github.com/yamahata/linux-umem.git linux-umem-oct-29-2012
> 
> Major changes v2 -> v3:
> - implemented pre+post optimization
> - auto detection of postcopy by incoming side
> - using threads on destination instead of fork
> - using blocking io instead of select + non-blocking io loop
> - less memory overhead
> - various improvement and code simplification
> - kernel module name change umem -> uvmem to avoid name conflict.
> 
> Patches organization:
> 1-2: trivial fixes
> 3-5: prepartion for threading. cherry-picked from migration tree
> 6-18: refactoring existing code and preparation
> 19-25: implement postcopy live migration itself (essential part)
> 26-35: optimization/heuristic for postcopy
> 
> Usage
> =====
> You need load uvmem character device on the host before starting migration.
> Postcopy can be used for tcg and kvm accelarator. The implementation depend
> on only linux uvmem character device. But the driver dependent code is split
> into a file.
> I tested only host page size == guest page size case, but the implementation
> allows host page size != guest page size case.
> 
> The following options are added with this patch series.
> - incoming part
>   use -incoming as usual. Postcopy is automatically detected.
>   example:
>   qemu -incoming tcp:0:4444 -monitor stdio -machine accel=kvm
> 
> - outging part
>   options for migrate command
>   migrate [-p [-n] [-m]] URI 
>           [<precopy count> [<prefault forward> [<prefault backword>]]]
> 
>   Newly added options/arguments
>   -p: indicate postcopy migration
>   -n: disable background transferring pages: This is for benchmark/debugging
>   -m: move background transfer of postcopy mode
>   <precopy count>: The number of precopy RAM scan before postcopy.
>                    default 0 (0 means no precopy)
>   <prefault forward>: The number of forward pages which is sent with on-demand
>   <prefault backward>: The number of backward pages which is sent with
>                        on-demand
> 
>   example:
>   migrate -p -n tcp:<dest ip address>:4444
>   migrate -p -n -m tcp:<dest ip address>:4444 42 42 0
> 
> 
> TODO
> ====
> - benchmark/evaluation
> - improve/optimization
>   At the moment at least what I'm aware of is
>   - pre+post case
>     On desitnation side reading dirty bitmap would cause long latency.
>     create thread for that.
> - consider on FUSE/CUSE possibility
> 
> basic postcopy work flow
> ========================
>         qemu on the destination
>               |
>               V
>         open(/dev/uvmem)
>               |
>               V
>         UVMEM_INIT
>               |
>               V
>         Here we have two file descriptors to
>         umem device and shmem file
>               |
>               |                                  umem threads
>               |                                  on the destination
>               |
>               V    create pipe to communicate
>         crete threads--------------------------------,
>               |                                      |
>               V                                   mmap(shmem file)
>         mmap(uvmem device) for guest RAM          close(shmem file)
>               |                                      |
>               |                                      |
>               V                                      |
>         wait for ready from daemon <----pipe-----send ready message
>               |                                      |
>               |                                 Here the daemon takes over
>         send ok------------pipe---------------> the owner of the socket
>               |                                       to the source
>               V                                      |
>         entering post copy stage                     |
>         start guest execution                        |
>               |                                      |
>               V                                      V
>         access guest RAM                          read() to get faulted pages
>               |                                      |
>               V                                      V
>         page fault ------------------------------>page offset is returned
>         block                                        |
>                                                      V
>                                                   pull page from the source
>                                                   write the page contents
>                                                   to the shmem.
>                                                      |
>                                                      V
>         unblock     <-----------------------------write() to tell served pages
>         the fault handler returns the page           |
>         page fault is resolved                       |
>               |                                      V
>               |                                   touch guest RAM pages
>               |                                      |
>               |                                      V
>               |                                   release the cached page
>               |                                   madvise(MADV_REMOVE)
>             |
>             |
>               |                                   pages can be sent
>               |                                   backgroundly
>               |                                      |
>               |                                      V
>               |                                   mark page is cached
>               |                                   Thus future page fault is
>               |                                   avoided.
>               |                                      |
>               |                                      V
>               |                                   touch guest RAM pages
>               |                                      |
>               |                                      V
>               |                                   release the cached page
>               |                                   madvise(MADV_REMOVE)
>               |                                      |
>               V                                      V
> 
>                  all the pages are pulled from the source
> 
>               |                                      |
>               V                                      V
>         migration completes                        exit()
> 
> 
> Isaku Yamahata (32):
>   migration.c: remove redundant line in migrate_init()
>   arch_init: DPRINTF format error and typo
>   osdep: add qemu_read_full() to read interrupt-safely
>   savevm: export qemu_peek_buffer, qemu_peek_byte, qemu_file_skip,
>     qemu_fflush
>   savevm/QEMUFile: consolidate QEMUFile functions a bit
>   savevm/QEMUFile: introduce qemu_fopen_fd
>   savevm/QEMUFile: add read/write QEMUFile on memory buffer
>   savevm, buffered_file: introduce method to drain buffer of buffered
>     file
>   arch_init: export RAM_SAVE_xxx flags for postcopy
>   arch_init/ram_save: introduce constant for ram save version = 4
>   arch_init: refactor ram_save_block() and export ram_save_block()
>   arch_init/ram_save_setup: factor out bitmap alloc/free
>   arch_init/ram_load: refactor ram_load
>   arch_init: factor out logic to find ram block with id string
>   migration: export migrate_fd_completed() and migrate_fd_cleanup()
>   uvmem.h: import Linux uvmem.h and teach update-linux-headers.sh
>   osdep: add QEMU_MADV_REMOVE and tirivial fix
>   postcopy: introduce helper functions for postcopy
>   savevm: add new section that is used by postcopy
>   postcopy: implement incoming part of postcopy live migration
>   postcopy outgoing: add -p option to migrate command
>   postcopy: implement outgoing part of postcopy live migration
>   postcopy/outgoing: add -n options to disable background transfer
>   postcopy/outgoing: implement forward/backword prefault
>   arch_init: factor out setting last_block, last_offset
>   postcopy/outgoing: add movebg mode(-m) to migration command
>   arch_init: factor out ram_load
>   arch_init: export ram_save_iterate()
>   postcopy: pre+post optimization incoming side
>   arch_init: export migration_bitmap_sync and helper method to get
>     bitmap
>   postcopy/outgoing: introduce precopy_count parameter
>   postcopy: pre+post optimization outgoing side
> 
> Paolo Bonzini (1):
>   split MRU ram list
> 
> Umesh Deshpande (2):
>   add a version number to ram_list
>   protect the ramlist with a separate mutex
> 
>  Makefile.target                 |    2 +
>  arch_init.c                     |  391 +++++---
>  arch_init.h                     |   24 +
>  buffered_file.c                 |   59 +-
>  buffered_file.h                 |    1 +
>  cpu-all.h                       |   16 +-
>  exec.c                          |   62 +-
>  hmp-commands.hx                 |   21 +-
>  hmp.c                           |   12 +-
>  linux-headers/linux/uvmem.h     |   41 +
>  migration-exec.c                |    8 +-
>  migration-fd.c                  |   23 +-
>  migration-postcopy.c            | 2019 
> +++++++++++++++++++++++++++++++++++++++
>  migration-tcp.c                 |   16 +-
>  migration-unix.c                |   36 +-
>  migration.c                     |   65 +-
>  migration.h                     |   42 +
>  osdep.c                         |   24 +
>  osdep.h                         |   13 +-
>  qapi-schema.json                |    6 +-
>  qemu-common.h                   |    2 +
>  qemu-file.h                     |   12 +-
>  qmp-commands.hx                 |    4 +-
>  savevm.c                        |  223 ++++-
>  scripts/update-linux-headers.sh |    2 +-
>  sysemu.h                        |    2 +-
>  umem.c                          |  291 ++++++
>  umem.h                          |   88 ++
>  vl.c                            |    5 +-
>  29 files changed, 3265 insertions(+), 245 deletions(-)
>  create mode 100644 linux-headers/linux/uvmem.h
>  create mode 100644 migration-postcopy.c
>  create mode 100644 umem.c
>  create mode 100644 umem.h
> 
> --
> 1.7.10.4
>