Re: [Qemu-devel] [PATCH v9 0/8] calculate blocktime for postcopy live migration

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Alexey Perevalov (a.perevalov@samsung.com) wrote:
> This is 9th version.
> 
> The rationale for that idea is following:
> vCPU could suspend during postcopy live migration until faulted
> page is not copied into kernel. Downtime on source side it's a value -
> time interval since source turn vCPU off, till destination start runnig
> vCPU. But that value was proper value for precopy migration it really shows
> amount of time when vCPU is down. But not for postcopy migration, because
> several vCPU threads could susppend after vCPU was started. That is important
> to estimate packet drop for SDN software.

Hi Alexey,
  I see that the UFFD_FEATURE_THREAD_ID has landed in kernel v4.14-rc1
over the weekend, so it's probably time to reheat this patchset.

  I think you should be able to generate a first patch by running
  scripts/update-linux-headers.sh

Dave

> (V8 -> V9)
>     - rebase
>     - traces
> 
> (V7 -> V8)
>     - just one comma in
> "migration: fix hardcoded function name in error report"
> It was really missed, but fixed in futher patch.
> 
> (V6 -> V7)
>     - copied bitmap was placed into RAMBlock as another migration
> related bitmaps.
>     - Ordering of mark_postcopy_blocktime_end call and ordering
> of checking copied bitmap were changed.
>     - linewrap style defects
>     - new patch "postcopy_place_page factoring out"
>     - postcopy_ram_supported_by_host accepts
> MigrationIncomingState in qmp_migrate_set_capabilities
>     - minor fixes of documentation. 
>     and huge description of get_postcopy_total_blocktime was
> moved. Davids comment.
> 
> (V5 -> V6)
>     - blocktime was added into hmp command. Comment from David.
>     - bitmap for copied pages was added as well as check in *_begin/_end
> functions. Patch uses just introduced RAMBLOCK_FOREACH. Comment from David.
>     - description of receive_ufd_features/request_ufd_features. Comment from David.
>     - commit message headers/@since references were modified. Comment from Eric.
>     - also typos in documentation. Comment from Eric.
>     - style and description of field in MigrationInfo. Comment from Eric.
>     - ufd_check_and_apply (former ufd_version_check) is calling twice,
> so my previous patch contained double allocation of blocktime context and
> as a result memory leak. In this patch series it was fixed.
> 
> (V4 -> V5)
>     - fill_destination_postcopy_migration_info empty stub was missed for none linux
> build
> 
> (V3 -> V4)
>     - get rid of Downtime as a name for vCPU waiting time during postcopy migration
>     - PostcopyBlocktimeContext renamed (it was just BlocktimeContext)
>     - atomic operations are used for dealing with fields of PostcopyBlocktimeContext
> affected in both threads.
>     - hardcoded function names in error_report were replaced to %s and __line__
>     - this patch set includes postcopy-downtime capability, but it used on
> destination, coupled with not possibility to return calculated downtime back
> to source to show it in query-migrate, it looks like a big trade off
>     - UFFD_API have to be sent notwithstanding need or not to ask kernel
> for a feature, due to kernel expects it in any case (see patch comment)
>     - postcopy_downtime included into query-migrate output
>     - also this patch set includes trivial fix
> migration: fix hardcoded function name in error report
> maybe that is a candidate for qemu-trivial mailing list, but I already
> sent "migration: Fixed code style" and it was unclaimed.
> 
> (V2 -> V3)
>     - Downtime calculation approach was changed, thanks to Peter Xu
>     - Due to previous point no more need to keep GTree as well as bitmap of cpus.
> So glib changes aren't included in this patch set, it could be resent in
> another patch set, if it will be a good reason for it.
>     - No procfs traces in this patchset, if somebody wants it, you could get it
> from patchwork site to track down page fault initiators.
>     - UFFD_FEATURE_THREAD_ID is requesting only when kernel supports it
>     - It doesn't send back the downtime, just trace it
> 
> This patch set is based on commit
> [PATCH v3 0/3] Add bitmap for received pages in postcopy migration
> 
> 
> Alexey Perevalov (8):
>   userfault: add pid into uffd_msg & update UFFD_FEATURE_*
>   migration: pass MigrationIncomingState* into migration check functions
>   migration: fix hardcoded function name in error report
>   migration: split ufd_version_check onto receive/request features part
>   migration: introduce postcopy-blocktime capability
>   migration: add postcopy blocktime ctx into MigrationIncomingState
>   migration: calculate vCPU blocktime on dst side
>   migration: postcopy_blocktime documentation
> 
>  docs/devel/migration.txt          |  10 ++
>  linux-headers/linux/userfaultfd.h |   4 +
>  migration/migration.c             |  12 +-
>  migration/migration.h             |   9 ++
>  migration/postcopy-ram.c          | 300 ++++++++++++++++++++++++++++++++++++--
>  migration/postcopy-ram.h          |   2 +-
>  migration/savevm.c                |   2 +-
>  migration/trace-events            |   5 +-
>  qapi-schema.json                  |   5 +-
>  9 files changed, 334 insertions(+), 15 deletions(-)
> 
> -- 
> 1.8.3.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK