Re: [Qemu-devel] [PATCH 16/17] migration: adjust migration_thread() process for page flipping

[Lei Li <lilei@linux.vnet.ibm.com>]

On 11/26/2013 10:11 PM, Paolo Bonzini wrote:
> Il 26/11/2013 14:53, Lei Li ha scritto:
>> 1) ram_save_setup stage, it will send all the bytes in this stages
>>     to destination, and send_pipefd by ram_control_before_iterate
>>     at the end of it.
> ram_save_setup runs doesn't send anything from guest RAM.  It sends the
> lengths of the various blocks.  As you said, at the end of
> ram_save_setup you send the pipefd.
>
> ram_save_iterate runs before ram_save_complete.  ram_save_iterate and
> ram_save_complete write data with exactly the same format.  Both of them
> can use ram_save_page
>
> It should not matter if some pages are sent as part of ram_save_iterate
> and others as part of ram_save_complete.
>
> One possibility is that you are hitting a bug due to the way you ignore
> the "0x01" byte that send_pipefd places on the socket.
>
>>> Oops.  I might have said this before thinking about postcopy and/or
>>> before seeing the benchmark results from Juan's patches.  If this part
>>> of the patch is just an optimization, I'd rather leave it out for now.
>> I am afraid that page flipping can not proceed correctly without this..
> I really would like to understand why, because it really shouldn't (this
> shouldn't be a place where you need a hook).

Hi Paolo,

Sorry for the late reply.

Yes, you are right!!  I just have a try with this adjustment removed, it
works well...

I remembered that it can not proceed correctly when debugging in previous
version without this as in theory it should like your explanation above. I
guess the only answer is that there was a bug regarding the one byte fd
control message just like the possibility you listed!
  

>
> Paolo
>
>


-- 
Lei