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Re: [Qemu-devel] [PATCH 00/21][RFC] postcopy live migration
From: |
Orit Wasserman |
Subject: |
Re: [Qemu-devel] [PATCH 00/21][RFC] postcopy live migration |
Date: |
Sun, 01 Jan 2012 11:43:34 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111115 Thunderbird/8.0 |
On 12/30/2011 12:39 AM, Anthony Liguori wrote:
> On 12/28/2011 07:25 PM, Isaku Yamahata wrote:
>> Intro
>> =====
>> This patch series implements postcopy live migration.[1]
>> As discussed at KVM forum 2011, dedicated character device is used for
>> distributed shared memory between migration source and destination.
>> Now we can discuss/benchmark/compare with precopy. I believe there are
>> much rooms for improvement.
>>
>> [1] http://wiki.qemu.org/Features/PostCopyLiveMigration
>>
>>
>> Usage
>> =====
>> You need load umem character device on the host before starting migration.
>> Postcopy can be used for tcg and kvm accelarator. The implementation depend
>> on only linux umem character device. But the driver dependent code is split
>> into a file.
>> I tested only host page size == guest page size case, but the implementation
>> allows host page size != guest page size case.
>>
>> The following options are added with this patch series.
>> - incoming part
>> command line options
>> -postcopy [-postcopy-flags<flags>]
>> where flags is for changing behavior for benchmark/debugging
>> Currently the following flags are available
>> 0: default
>> 1: enable touching page request
>>
>> example:
>> qemu -postcopy -incoming tcp:0:4444 -monitor stdio -machine accel=kvm
>>
>> - outging part
>> options for migrate command
>> migrate [-p [-n]] URI
>> -p: indicate postcopy migration
>> -n: disable background transferring pages: This is for benchmark/debugging
>>
>> example:
>> migrate -p -n tcp:<dest ip address>:4444
>>
>>
>> TODO
>> ====
>> - benchmark/evaluation. Especially how async page fault affects the result.
>
> I'll review this series next week (Mike/Juan, please also review when you
> can).
>
> But we really need to think hard about whether this is the right thing to
> take into the tree. I worry a lot about the fact that we don't test pre-copy
> migration nearly enough and adding a second form just introduces more things
> to test.
>
> It's also not clear to me why post-copy is better. If you were going to sit
> down and explain to someone building a management tool when they should use
> pre-copy and when they should use post-copy, what would you tell them?
Start with pre-copy , if it doesn't converge switch to post-copy
Orit
>
> Regards,
>
> Anthony Liguori
>
- Re: [Qemu-devel] [PATCH 00/21][RFC] postcopy live migration,
Orit Wasserman <=