Re: [Qemu-devel] Re: [PATCH 0/4] Threaded tcp incoming migration.

[Anthony Liguori <aliguori@linux.vnet.ibm.com>]

On 06/01/2010 11:18 AM, Yoshiaki Tamura wrote:
> 2010/6/2 Anthony Liguori<aliguori@linux.vnet.ibm.com>:
>    
>> On 06/01/2010 10:40 AM, Yoshiaki Tamura wrote:
>>      
>>> Hi,
>>>
>>> This series add threaded tcp incoming migration.  Currently, tcp migration
>>> on
>>> incoming side is blocked when outgoing has started on the remote side, and
>>> you
>>> can't do anything.  With this series you can get info of incoming
>>> migration by
>>> calling "info migrate" like on outgoing side.  Threaded tcp incoming
>>> migration
>>> is enable only when --enable-io-thread is set.
>>>
>>>        
>> I'm much less confident that threading is the answer here.  We really would
>> just need to have asynchronous incoming migration.
>>      
> You mean, go back to select() in main(), and then call incoming
> handler each time?
> Won't it introduce more latency, resulting less throughput?
>    

I wouldn't think so.  With threads, you've got to acquire locks and that 
lock acquisition can be a source of significant latency.  By blocking in 
select, you've got a straight dispatch path.

Really, we'd get 99% of the way there just focusing on live loading of 
ram.  There's really no need to make the final stage of migration live.

> Although threading maybe a big hammer for just getting monitor
> working, I think using thread for incoming handler may worth if it
> doesn't heart performance on receiving data.
>    

Unless I'm mistaken, the thread patches you've posted make no attempt at 
addressing the problem of locking.  I believe that properly handling 
locking would result in the patch series increasing in size and 
complexity rather significantly.

I think the simpler approach is to implement a state machine for ram 
loading.

Regards,

Anthony Liguori

> The downside is mutual exclusion, of course...
>
> Thanks,
>
> Yoshi
>
>    
>> Regards,
>>
>> Anthony Liguori
>>
>>      
>>> This series apply on top of patch from Corentin posted on May 29.
>>>
>>> http://www.mail-archive.com/qemu-devel@nongnu.org/msg33830.html
>>>
>>> Yoshiaki Tamura (4):
>>>    qemu-thread: add qemu_thread_join().
>>>    migration-tcp: threaded tcp incoming migration.
>>>    arch_init: calculate transferred bytes at ram_load().
>>>    migration: add support to print migration info on incoming side.
>>>
>>>   arch_init.c     |    2 +
>>>   migration-tcp.c |   86
>>> ++++++++++++++++++++++++++++++++++++++++++++++---------
>>>   migration.c     |   18 +++++++++--
>>>   migration.h     |    2 +-
>>>   qemu-thread.c   |    9 ++++++
>>>   qemu-thread.h   |    1 +
>>>   6 files changed, 99 insertions(+), 19 deletions(-)
>>>
>>>
>>>        
>>
>>
>>