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


From: Cristian Klein
Subject: Re: [Qemu-devel] [PATCH v4 00/47] Postcopy implementation
Date: Tue, 7 Oct 2014 11:27:27 +0900

On 04 Oct 2014, at 4:21 , Dr. David Alan Gilbert <address@hidden> 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.

Cristian 

> * Dr. David Alan Gilbert (git) (address@hidden) wrote:
>> From: "Dr. David Alan Gilbert" <address@hidden>
>> 
>> 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 / address@hidden / Manchester, UK




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