[Qemu-devel] [PATCH v11 0/6] calculate blocktime for postcopy live migration

[Alexey Perevalov]

This is 11th 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.

(V11 -> V10)
    - rebase
    - update documentation (comment from David)
    - postcopy_notifier was removed from PostcopyBlocktimeContext (comment from
David)
    - fix "since 2.10" for postcopy-vcpu-blocktime (comment from Eric)
    - fix order in mark_postcopy_blocktime_begin/end (comment from David),
but I think it still have a slim race condition
    - remove error_report from fill_destination_postcopy_migration_info (comment
from David)

(V9 -> V10)
    - rebase
    - patch "update kernel header for UFFD_FEATURE_*" has changed,
and was generated by  scripts/update-linux-headers.sh as David suggested. 


(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 v10 0/3] Add bitmap for received pages in postcopy migration

Both patch sets were rebased on 
commit d147f7e815f97cb477e223586bcb80c316ae10ea

Alexey Perevalov (6):
  migration: introduce postcopy-blocktime capability
  migration: add postcopy blocktime ctx into MigrationIncomingState
  migration: calculate vCPU blocktime on dst side
  migration: postcopy_blocktime documentation
  migration: add blocktime calculation into postcopy-test
  migration: add postcopy total blocktime into query-migrate

 docs/devel/migration.txt |  13 +++
 hmp.c                    |  15 +++
 migration/migration.c    |  51 +++++++++-
 migration/migration.h    |  13 +++
 migration/postcopy-ram.c | 257 ++++++++++++++++++++++++++++++++++++++++++++++-
 migration/trace-events   |   6 +-
 qapi/migration.json      |  16 ++-
 tests/postcopy-test.c    |  63 +++++++++---
 8 files changed, 411 insertions(+), 23 deletions(-)

-- 
2.7.4