[PATCH 0/6] Introduce multifd zero page checking.

[Hao Xiang]

This patchset is based on Juan Quintela's old series here
https://lore.kernel.org/all/20220802063907.18882-1-quintela@redhat.com/

In the multifd live migration model, there is a single migration main
thread scanning the page map, queuing the pages to multiple multifd
sender threads. The migration main thread runs zero page checking on
every page before queuing the page to the sender threads. Zero page
checking is a CPU intensive task and hence having a single thread doing
all that doesn't scale well. This change introduces a new function
to run the zero page checking on the multifd sender threads. This
patchset also lays the ground work for future changes to offload zero
page checking task to accelerator hardwares.

Use two Intel 4th generation Xeon servers for testing.

Architecture:        x86_64
CPU(s):              192
Thread(s) per core:  2
Core(s) per socket:  48
Socket(s):           2
NUMA node(s):        2
Vendor ID:           GenuineIntel
CPU family:          6
Model:               143
Model name:          Intel(R) Xeon(R) Platinum 8457C
Stepping:            8
CPU MHz:             2538.624
CPU max MHz:         3800.0000
CPU min MHz:         800.0000

Perform multifd live migration with below setup:
1. VM has 100GB memory. All pages in the VM are zero pages.
2. Use tcp socket for live migratio.
3. Use 4 multifd channels and zero page checking on migration main thread.
4. Use 1/2/4 multifd channels and zero page checking on multifd sender
threads.
5. Record migration total time from sender QEMU console's "info migrate"
command.
6. Calculate throughput with "100GB / total time".

+------------------------------------------------------+
|zero-page-checking | total-time(ms) | throughput(GB/s)|
+------------------------------------------------------+
|main-thread        | 9629           | 10.38GB/s       |
+------------------------------------------------------+
|multifd-1-threads  | 6182           | 16.17GB/s       |
+------------------------------------------------------+
|multifd-2-threads  | 4643           | 21.53GB/s       |
+------------------------------------------------------+
|multifd-4-threads  | 4143           | 24.13GB/s       |
+------------------------------------------------------+

Apply this patchset on top of commit
39a6e4f87e7b75a45b08d6dc8b8b7c2954c87440

Hao Xiang (6):
  migration/multifd: Add new migration option multifd-zero-page.
  migration/multifd: Add zero pages and zero bytes counter to migration
    status interface.
  migration/multifd: Support for zero pages transmission in multifd
    format.
  migration/multifd: Zero page transmission on the multifd thread.
  migration/multifd: Enable zero page checking from multifd threads.
  migration/multifd: Add a new migration test case for legacy zero page
    checking.

 migration/migration-hmp-cmds.c |  11 ++++
 migration/multifd.c            | 106 ++++++++++++++++++++++++++++-----
 migration/multifd.h            |  22 ++++++-
 migration/options.c            |  20 +++++++
 migration/options.h            |   1 +
 migration/ram.c                |  49 ++++++++++++---
 migration/trace-events         |   8 +--
 qapi/migration.json            |  39 ++++++++++--
 tests/qtest/migration-test.c   |  26 ++++++++
 9 files changed, 249 insertions(+), 33 deletions(-)

-- 
2.30.2