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Re: [Qemu-ppc] [PATCH 7/8] pseries: savevm support for PAPR virtual SCSI

From: Alexey Kardashevskiy
Subject: Re: [Qemu-ppc] [PATCH 7/8] pseries: savevm support for PAPR virtual SCSI
Date: Fri, 31 May 2013 20:12:41 +1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6

On 05/31/2013 06:18 PM, Paolo Bonzini wrote:
> Il 31/05/2013 07:58, Alexey Kardashevskiy ha scritto:
>> On 05/27/2013 05:03 PM, Paolo Bonzini wrote:
>>> Il 27/05/2013 08:48, Alexey Kardashevskiy ha scritto:
>>>>>> This is only true when the rerror and werror options have the values
>>>>>> "ignore" or "report".  See virtio-scsi for an example of how to save the
>>>>>> requests using the save_request and load_request callbacks in 
>>>>>> SCSIBusInfo.
>>>> Sigh.
>>> ?
>> I thought the series is ready to go but I was wrong. Furthermore when I got
>> to the point where I could actually test the save/restore for vscsi_req,
>> migration was totally broken on PPC and it took some time to fix it :-/
> It is ready.  I was just pointing out that it's not _production_ ready.

What is the difference then? :)

> (Sorry, I'm unusually terse these days).
>> I run QEMU as (this is the destination, the source just does not have
>> -incoming):
>> ./qemu-system-ppc64 \
>>  -L "qemu-ppc64-bios/" \
>>  -device "spapr-vscsi,id=ibmvscsi0" \
>>  -drive
>> "file=virtimg/fc18guest,if=none,id=dddrive0,readonly=off,format=blkdebug,media=disk,werror=stop,rerror=stop"
>> \
>>  -device
>> "scsi-disk,id=scsidisk0,bus=ibmvscsi0.0,channel=0,scsi-id=0,lun=0,drive=dddrive0,removable=off"
>> \
>>  -incoming "tcp:localhost:4000" \
>>  -m "1024" \
>>  -machine "pseries" \
>>  -nographic \
>>  -vga "none" \
>>  -enable-kvm
>> Am I using werror/rerror correctly?
> Yes.
>> I did not really understand how to use blkdebug or what else to hack in
>> raw-posix but the point is I cannot get QEMU into a state with at least one
>> vcsci_req.active==1, they are always inactive no matter what I do - I run
>> 10 instances of "dd if=/def/sda of=/dev/null bs=4K" (on 8GB image with
>> FC18) and increase migration speed to 500MB/s, no effect.
> No, that doesn't help.
>> How do you trigger the situation when there are inactive requests which
>> have to be migrated?
> You need to trigger an error.  For example, you could use a sparse image
> on an almost-full partition and let "dd" fill your disk.  Then migrate
> to another instance of QEMU on the same machine, the destination machine
> should succeed migration but fail starting the machine.

Why would it fail? I run "dd", it fills the disk and stops. Then I migrate.
How can I get pending SCSI request in a queue? Sorry, I am definitely
missing something.

> When free space
> on that partition, and "cont" on the destination, it should resume.
>> And another question (sorry I am not very familiar with terminology but
>> cc:Ben is :) ) - what happens with indirect requests if migration happened
>> in the middle of handling such a request? virtio-scsi does not seem to
>> handle this situation anyhow, it just reconstructs the whole request and
>> that's it.
> What are indirect requests?

I'll leave it to Ben to avoid confusing :)


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