[Qemu-devel] [RFC PATCH v6 0/3] Throttle-down guest to help with live migration convergence

[Chegu Vinod <chegu_vinod@hp.com>]

Busy enterprise workloads hosted on large sized VM's tend to dirty
memory faster than the transfer rate achieved via live guest migration.
Despite some good recent improvements (& using dedicated 10Gig NICs
between hosts) the live migration does NOT converge.

If a user chooses to force convergence of their migration via a new
migration capability "auto-converge" then this change will auto-detect
lack of convergence scenario and trigger a slow down of the workload
by explicitly disallowing the VCPUs from spending much time in the VM
context.

The migration thread tries to catchup and this eventually leads
to convergence in some "deterministic" amount of time. Yes it does
impact the performance of all the VCPUs but in our observation that
lasts only for a short duration of time. i.e. end up entering
stage 3 (downtime phase) soon after that. No external monitoring/triggers
are required.

Thanks to Juan and Paolo for their useful suggestions.

---
Changes from v5:
- incorporated feedback from Paolo & Igor.
- rebased to latest qemu.git

Changes from v4:
- incorporated feedback from Paolo.
- split into 3 patches.

Changes from v3:
- incorporated feedback from Paolo and Eric
- rebased to latest qemu.git

Changes from v2:
- incorporated feedback from Orit, Juan and Eric
- stop the throttling thread at the start of stage 3
- rebased to latest qemu.git

Changes from v1:
- rebased to latest qemu.git
- added auto-converge capability(default off) - suggested by Anthony Liguori &
                                                Eric Blake.

Signed-off-by: Chegu Vinod <chegu_vinod@hp.com>
---

Chegu Vinod (3):
  Introduce async_run_on_cpu()
  Add 'auto-converge' migration capability
  Force auto-convegence of live migration

 arch_init.c                   |   85 +++++++++++++++++++++++++++++++++++++++++
 cpus.c                        |   29 ++++++++++++++
 include/migration/migration.h |    2 +
 include/qemu-common.h         |    1 +
 include/qom/cpu.h             |   10 +++++
 migration.c                   |    9 ++++
 qapi-schema.json              |    5 ++-
 7 files changed, 140 insertions(+), 1 deletions(-)