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Re: [Qemu-devel] [PATCH 16/17] migration: adjust migration_thread() proc

From: Lei Li
Subject: Re: [Qemu-devel] [PATCH 16/17] migration: adjust migration_thread() process for page flipping
Date: Thu, 28 Nov 2013 16:19:47 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0

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!



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