Re: [Qemu-devel] [PATCH v4 00/47] Postcopy implementation

[Cristian Klein <cristian.klein@cs.umu.se>]

On 07 Oct 2014, at 17:12 , Dr. David Alan Gilbert <dgilbert@redhat.com> wrote:

> * Cristian Klein (cristian.klein@cs.umu.se) wrote:
>> On 04 Oct 2014, at 4:21 , Dr. David Alan Gilbert <dgilbert@redhat.com> wrote:
>> 
>>> 
>>> I've updated our github at:
>>> https://github.com/orbitfp7/qemu/tree/wp3-postcopy
>>> 
>>> to have this version.
>>> 
>>> and it corresponds to the tag:
>>> https://github.com/orbitfp7/qemu/releases/tag/wp3-postcopy-v4
>> 
>> Hi Dave,
>> 
>> I just tested this version of post-copy using the libvirt patches I recently posted and it works a lot better. The video streaming VM migrates with a downtime of less than 1 second. Before post-copy finishes, the VM is a bit slow but otherwise running well.
>> 
>> I also tested the patches with a VM doing ?ping? and the downtime was around 0.6 seconds. I suspect that this delay could be caused by libvirt and not by qemu. Notice that, libvirt is a bit special, in the sense that the VM is migrated in suspended state and resumed only after the network was set up on the destination. I will investigate and let you know.
> 
> That's great news - although I'm not quite sure what caused the improvement, there
> were quite a few minor bug fixes and things but nothing that I can think of that
> would directly contribute (except the patches I'd sent you which you'd already tried).

Unfortunately, I made an error in my experiments (post-copy started too late). I re-launched the experiments a few times. A ping VM observes a downtime of about 2 seconds, whereas a video streaming VM of about 4 seconds.

Cristian

>> 
>>> * Dr. David Alan Gilbert (git) (dgilbert@redhat.com) wrote:
>>>> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>>>> 
>>>> Hi,
>>>> This is the 4th cut of my version of postcopy; it is designed for use with
>>>> the Linux kernel additions just posted by Andrea Arcangeli here:
>>>> 
>>>> http://marc.info/?l=linux-kernel&m=141235633015100&w=2
>>>> 
>>>> (Note: This is a new version compared to my previous postcopy patchset; you'll
>>>> need to update the kernel to the new version.)
>>>> 
>>>> Other than the new kernel ABI (which is only a small change to the userspace side);
>>>> the major changes are;
>>>> 
>>>> a) Code for host page size != target page size
>>>> b) Support for migration over fd 
>>>>    From Cristian Klein; this is for libvirt support which Cristian recently
>>>>    posted to the libvirt list.
>>>> c) It's now build bisectable and builds on 32bit
>>>> 
>>>> Testing wise; I've now done many thousand of postcopy migrations without
>>>> failure (both of idle and busy guests); so it seems pretty solid.
>>>> 
>>>> Must-TODO's:
>>>> 1) A partially repeatable migration_cancel failure
>>>> 2) virt_test's migrate.with_reboot test is failing
>>>> 3) The ACPI fix in 2.1 that allowed migrating RAMBlocks to be larger than
>>>>   the source feels like it needs looking at for postcopy.
>>>> 4) Paolo's comments with respect to the wakeup_request/is_running code
>>>>    in the migration thread
>>>> 5) xbzrle needs disabling once in postcopy
>>>> 
>>>> Later-TODO's:
>>>> 1) Control the rate of background page transfers during postcopy to
>>>>    reduce their impact on the latency of postcopy requests.
>>>> 2) Work with RDMA
>>>> 3) Could destination RP be made blocking (as per discussion with Paolo;
>>>>    I'm still worried that that changes too many assumptions)
>>>> 
>>>> 
>>>> 
>>>> V4:
>>>> Initial support for host page size != target page size
>>>>   - tested heavily on hps==tps
>>>>   - only partially tested on hps!=tps systems
>>>>   - This involved quite a bit of rework around the discard code
>>>> Updated to new kernel userfault ABI
>>>>   - It won't work with the previous version
>>>> Fix mis-optimisation of postcopy request for wrong RAMBlock
>>>>    request for block A offset n
>>>>    un-needed fault for block B/m (already received - no req sent)
>>>>    request for block B/l  - wrongly sent as request for A/l
>>>> Fix thinko in discard bitmap processing (missed last word of bitmap)
>>>>    Symptom: remap failures near the top of RAM if postcopy started late
>>>> Fix bug that caused kernel page acknowledgments to be misaligned
>>>>    May have meant the guest was paused for longer than required
>>>> Fix potential for crashing cleaning up failed RP
>>>> Fixes in docs (from Yang)
>>>> Handle migration by fd as sockets if they are sockets
>>>> Build tested on 32bit
>>>> Fully build bisectable (x86-64)
>>>> 
>>>> 
>>>> Dave
>>>> 
>>>> Cristian Klein (1):
>>>> Handle bi-directional communication for fd migration
>>>> 
>>>> Dr. David Alan Gilbert (46):
>>>> QEMUSizedBuffer based QEMUFile
>>>> Tests: QEMUSizedBuffer/QEMUBuffer
>>>> Start documenting how postcopy works.
>>>> qemu_ram_foreach_block: pass up error value, and down the ramblock
>>>>   name
>>>> improve DPRINTF macros, add to savevm
>>>> Add qemu_get_counted_string to read a string prefixed by a count byte
>>>> Create MigrationIncomingState
>>>> socket shutdown
>>>> Provide runtime Target page information
>>>> Return path: Open a return path on QEMUFile for sockets
>>>> Return path: socket_writev_buffer: Block even on non-blocking fd's
>>>> Migration commands
>>>> Return path: Control commands
>>>> Return path: Send responses from destination to source
>>>> Return path: Source handling of return path
>>>> qemu_loadvm errors and debug
>>>> ram_debug_dump_bitmap: Dump a migration bitmap as text
>>>> Rework loadvm path for subloops
>>>> Add migration-capability boolean for postcopy-ram.
>>>> Add wrappers and handlers for sending/receiving the postcopy-ram
>>>>   migration messages.
>>>> QEMU_VM_CMD_PACKAGED: Send a packaged chunk of migration stream
>>>> migrate_init: Call from savevm
>>>> Allow savevm handlers to state whether they could go into postcopy
>>>> postcopy: OS support test
>>>> migrate_start_postcopy: Command to trigger transition to postcopy
>>>> MIG_STATE_POSTCOPY_ACTIVE: Add new migration state
>>>> qemu_savevm_state_complete: Postcopy changes
>>>> Postcopy page-map-incoming (PMI) structure
>>>> Postcopy: Maintain sentmap and calculate discard
>>>> postcopy: Incoming initialisation
>>>> postcopy: ram_enable_notify to switch on userfault
>>>> Postcopy: Postcopy startup in migration thread
>>>> Postcopy: Create a fault handler thread before marking the ram as
>>>>   userfault
>>>> Page request:  Add MIG_RPCOMM_REQPAGES reverse command
>>>> Page request: Process incoming page request
>>>> Page request: Consume pages off the post-copy queue
>>>> Add assertion to check migration_dirty_pages
>>>> postcopy_ram.c: place_page and helpers
>>>> Postcopy: Use helpers to map pages during migration
>>>> qemu_ram_block_from_host
>>>> Don't sync dirty bitmaps in postcopy
>>>> Host page!=target page: Cleanup bitmaps
>>>> Postcopy; Handle userfault requests
>>>> Start up a postcopy/listener thread ready for incoming page data
>>>> postcopy: Wire up loadvm_postcopy_ram_handle_{run,end} commands
>>>> End of migration for postcopy
>>>> 
>>>> Makefile.objs                    |    2 +-
>>>> arch_init.c                      |  739 +++++++++++++++++++++++++--
>>>> docs/migration.txt               |  189 +++++++
>>>> exec.c                           |   76 ++-
>>>> hmp-commands.hx                  |   15 +
>>>> hmp.c                            |    7 +
>>>> hmp.h                            |    1 +
>>>> include/exec/cpu-common.h        |    8 +-
>>>> include/migration/migration.h    |  130 +++++
>>>> include/migration/postcopy-ram.h |  106 ++++
>>>> include/migration/qemu-file.h    |   47 ++
>>>> include/migration/vmstate.h      |    2 +-
>>>> include/qemu/sockets.h           |    1 +
>>>> include/qemu/typedefs.h          |    9 +-
>>>> include/sysemu/sysemu.h          |   43 +-
>>>> migration-fd.c                   |   24 +-
>>>> migration-rdma.c                 |    4 +-
>>>> migration.c                      |  693 +++++++++++++++++++++++++-
>>>> postcopy-ram.c                   | 1016 ++++++++++++++++++++++++++++++++++++++
>>>> qapi-schema.json                 |   14 +-
>>>> qemu-file.c                      |  598 +++++++++++++++++++++-
>>>> qmp-commands.hx                  |   19 +
>>>> savevm.c                         |  881 +++++++++++++++++++++++++++++++--
>>>> tests/Makefile                   |    2 +-
>>>> tests/test-vmstate.c             |   74 +--
>>>> util/qemu-sockets.c              |   28 ++
>>>> 26 files changed, 4550 insertions(+), 178 deletions(-)
>>>> create mode 100644 include/migration/postcopy-ram.h
>>>> create mode 100644 postcopy-ram.c
>>>> 
>>>> -- 
>>>> 1.9.3
>>>> 
>>>> 
>>> --
>>> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>> 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK