Re: [Qemu-devel] [PATCH COLO-Frame v5 00/29] COarse-grain LOck-stepping(COLO) Virtual Machines for Non-stop Service

[Wen Congyang]

On 05/29/2015 12:24 AM, Dr. David Alan Gilbert wrote:
> * zhanghailiang (address@hidden) wrote:
>> This is the 5th version of COLO, here is only COLO frame part, include: VM 
>> checkpoint,
>> failover, proxy API, block replication API, not include block replication.
>> The block part has been sent by wencongyang:
>> "[Qemu-devel] [PATCH COLO-Block v5 00/15] Block replication for continuous 
>> checkpoints"
>>
>> we have finished some new features and optimization on COLO (As a 
>> development branch in github),
>> but for easy of review, it is better to keep it simple now, so we will not 
>> add too much new 
>> codes into this frame patch set before it been totally reviewed. 
>>
>> You can get the latest integrated qemu colo patches from github (Include 
>> Block part):
>> https://github.com/coloft/qemu/commits/colo-v1.2-basic
>> https://github.com/coloft/qemu/commits/colo-v1.2-developing (more features)
>>
>> Please NOTE the difference between these two branch.
>> colo-v1.2-basic is exactly same with this patch series, which has basic 
>> features of COLO.
>> Compared with colo-v1.2-basic, colo-v1.2-developing has some optimization in 
>> the 
>> process of checkpoint, including: 
>>    1) separate ram and device save/load process to reduce size of extra 
>> memory
>>       used during checkpoint
>>    2) live migrate part of dirty pages to slave during sleep time.
>> Besides, we add some statistic info in colo-v1.2-developing, which you can 
>> get these stat
>> info by using command 'info migrate'.
> 
> 
> Hi,
>   I have that running now.
> 
> Some notes:
>   1) The colo-proxy is working OK until qemu quits, and then it gets an RCU 
> problem; see below
>   2) I've attached some minor tweaks that were needed to build with the 4.1rc 
> kernel I'm using;
>      they're very minor changes and I don't think related to (1).
>   3) I've also included some minor fixups I needed to get the -developing 
> world
>      to build;  my compiler is fussy about unused variables etc - but I think 
> the code
>      in ram_save_complete in your -developing patch is wrong because there 
> are two
>      'pages' variables and the one in the inner loop is the only one changed.
>   4) I've started trying simple benchmarks and tests now:
>     a) With a simple web server most requests have very little overhead, the 
> comparison
>        matches most of the time;  I do get quite large spikes (0.04s->1.05s) 
> which I guess
>        corresponds to when a checkpoint happens, but I'm not sure why the 
> spike is so big,
>        since the downtime isn't that big.

I reproduce it, and we are investigating it now.

>     b) I tried something with more dynamic pages - the front page of a simple 
> bugzilla

What does 'dynamic pages' mean?

>        install;  it failed the comparison every time; it took me a while to 
> figure out
>        why, but it generates a unique token in it's javascript each time (for 
> a password reset
>        link), and I guess the randomness used by that doesn't match on the 
> two hosts.

Yes.

Thanks
Wen Congyang

>        It surprised me, because I didn't expect this page to have much 
> randomness
>        in.
> 
>   4a is really nice - it shows the benefit of COLO over the simple 
> checkpointing;
> checkpoints happen very rarely.
> 
> The colo-proxy rcu problem I hit shows as rcu-stalls in both primary and 
> secondary
> after the qemu quits; the backtrace of the qemu stack is:
> 
> [<ffffffff810d8c0c>] wait_rcu_gp+0x5c/0x80
> [<ffffffff810ddb05>] synchronize_rcu+0x45/0xd0
> [<ffffffffa0a251e5>] colo_node_release+0x35/0x50 [nfnetlink_colo]
> [<ffffffffa0a25795>] colonl_close_event+0xe5/0x160 [nfnetlink_colo]
> [<ffffffff81090c96>] notifier_call_chain+0x66/0x90
> [<ffffffff8109154c>] atomic_notifier_call_chain+0x6c/0x110
> [<ffffffff815eee07>] netlink_release+0x5b7/0x7f0
> [<ffffffff815878bf>] sock_release+0x1f/0x90
> [<ffffffff81587942>] sock_close+0x12/0x20
> [<ffffffff812193c3>] __fput+0xd3/0x210
> [<ffffffff8121954e>] ____fput+0xe/0x10
> [<ffffffff8108d9f7>] task_work_run+0xb7/0xf0
> [<ffffffff81002d4d>] do_notify_resume+0x8d/0xa0
> [<ffffffff81722b66>] int_signal+0x12/0x17
> [<ffffffffffffffff>] 0xffffffffffffffff
> 
> that's with both the 423a8e268acbe3e644a16c15bc79603cfe9eb084 from yesterday 
> and 
> older e58e5152b74945871b00a88164901c0d46e6365e tags on colo-proxy.
> I'm not sure of the right fix; perhaps it might be possible to replace the 
> synchronize_rcu in colo_node_release by a call_rcu that does the kfree later?
> 
> Thanks,
> 
> Dave
> 
>>
>> You can test any branch of the above, 
>> about how to test COLO, Please reference to the follow link.
>> http://wiki.qemu.org/Features/COLO.
>>
>> COLO is still in early stage, 
>> your comments and feedback are warmly welcomed.
>>
>> Cc: address@hidden
>>
>> TODO:
>> 1. Strengthen failover
>> 2. COLO function switch on/off
>> 2. Optimize proxy part, include proxy script.
>>   1) Remove the limitation of forward network link.
>>   2) Reuse the nfqueue_entry and NF_STOLEN to enqueue skb
>> 3. The capability of continuous FT
>>
>> v5:
>> - Replace the previous communication way between proxy and qemu with 
>> nfnetlink
>> - Remove the 'forward device'parameter of xt_PMYCOLO, and now we use 
>> iptables command
>> to set the 'forward device'
>> - Turn DPRINTF into trace_ calls as Dave's suggestion
>>
>> v4:
>> - New block replication scheme (use image-fleecing for sencondary side)
>> - Adress some comments from Eric Blake and Dave
>> - Add commmand colo-set-checkpoint-period to set the time of periodic 
>> checkpoint
>> - Add a delay (100ms) between continuous checkpoint requests to ensure VM
>>   run 100ms at least since last pause.
>> v3:
>> - use proxy instead of colo agent to compare network packets
>> - add block replication
>> - Optimize failover disposal
>> - handle shutdown
>>
>> v2:
>> - use QEMUSizedBuffer/QEMUFile as COLO buffer
>> - colo support is enabled by default
>> - add nic replication support
>> - addressed comments from Eric Blake and Dr. David Alan Gilbert
>>
>> v1:
>> - implement the frame of colo
>>
>> Wen Congyang (1):
>>   COLO: Add block replication into colo process
>>
>> zhanghailiang (28):
>>   configure: Add parameter for configure to enable/disable COLO support
>>   migration: Introduce capability 'colo' to migration
>>   COLO: migrate colo related info to slave
>>   migration: Integrate COLO checkpoint process into migration
>>   migration: Integrate COLO checkpoint process into loadvm
>>   COLO: Implement colo checkpoint protocol
>>   COLO: Add a new RunState RUN_STATE_COLO
>>   QEMUSizedBuffer: Introduce two help functions for qsb
>>   COLO: Save VM state to slave when do checkpoint
>>   COLO RAM: Load PVM's dirty page into SVM's RAM cache temporarily
>>   COLO VMstate: Load VM state into qsb before restore it
>>   arch_init: Start to trace dirty pages of SVM
>>   COLO RAM: Flush cached RAM into SVM's memory
>>   COLO failover: Introduce a new command to trigger a failover
>>   COLO failover: Implement COLO master/slave failover work
>>   COLO failover: Don't do failover during loading VM's state
>>   COLO: Add new command parameter 'colo_nicname' 'colo_script' for net
>>   COLO NIC: Init/remove colo nic devices when add/cleanup tap devices
>>   COLO NIC: Implement colo nic device interface configure()
>>   COLO NIC : Implement colo nic init/destroy function
>>   COLO NIC: Some init work related with proxy module
>>   COLO: Handle nfnetlink message from proxy module
>>   COLO: Do checkpoint according to the result of packets comparation
>>   COLO: Improve checkpoint efficiency by do additional periodic
>>     checkpoint
>>   COLO: Add colo-set-checkpoint-period command
>>   COLO NIC: Implement NIC checkpoint and failover
>>   COLO: Disable qdev hotplug when VM is in COLO mode
>>   COLO: Implement shutdown checkpoint
>>
>>  arch_init.c                            | 243 +++++++++-
>>  configure                              |  36 +-
>>  hmp-commands.hx                        |  30 ++
>>  hmp.c                                  |  14 +
>>  hmp.h                                  |   2 +
>>  include/exec/cpu-all.h                 |   1 +
>>  include/migration/migration-colo.h     |  57 +++
>>  include/migration/migration-failover.h |  22 +
>>  include/migration/migration.h          |   3 +
>>  include/migration/qemu-file.h          |   3 +-
>>  include/net/colo-nic.h                 |  27 ++
>>  include/net/net.h                      |   3 +
>>  include/sysemu/sysemu.h                |   3 +
>>  migration/Makefile.objs                |   2 +
>>  migration/colo-comm.c                  |  68 +++
>>  migration/colo-failover.c              |  48 ++
>>  migration/colo.c                       | 836 
>> +++++++++++++++++++++++++++++++++
>>  migration/migration.c                  |  60 ++-
>>  migration/qemu-file-buf.c              |  58 +++
>>  net/Makefile.objs                      |   1 +
>>  net/colo-nic.c                         | 420 +++++++++++++++++
>>  net/tap.c                              |  45 +-
>>  qapi-schema.json                       |  42 +-
>>  qemu-options.hx                        |  10 +-
>>  qmp-commands.hx                        |  41 ++
>>  savevm.c                               |   2 +-
>>  scripts/colo-proxy-script.sh           |  88 ++++
>>  stubs/Makefile.objs                    |   1 +
>>  stubs/migration-colo.c                 |  58 +++
>>  trace-events                           |  11 +
>>  vl.c                                   |  39 +-
>>  31 files changed, 2235 insertions(+), 39 deletions(-)
>>  create mode 100644 include/migration/migration-colo.h
>>  create mode 100644 include/migration/migration-failover.h
>>  create mode 100644 include/net/colo-nic.h
>>  create mode 100644 migration/colo-comm.c
>>  create mode 100644 migration/colo-failover.c
>>  create mode 100644 migration/colo.c
>>  create mode 100644 net/colo-nic.c
>>  create mode 100755 scripts/colo-proxy-script.sh
>>  create mode 100644 stubs/migration-colo.c
>>
>> -- 
>> 1.7.12.4
>>
>>
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
>