Re: [RFC][PATCH 12/13] Kemari: use signal to save qemu state for Kemari

[Yoshiaki Tamura <tamura.yoshiaki@lab.ntt.co.jp>]

Keir Fraser wrote:
> On 18/03/2009 09:11, "Yoshiaki Tamura" <tamura.yoshiaki@lab.ntt.co.jp>
> wrote:
> 
>> Thanks for measuring the numbers.  It made things clear.
>> I think we need a signal-based interface as Ian said previously.
>>
>> On our test environment, AMD Barcelona 2.3GHz, the total cpu cycles of Kemari
>> in 
>> userland when running I/O intensive applications is around 3000000.
>> Although Xen transferring code and QEMU saving code is processed concurrently,
>> using xenstored for staring QEMU portion would lower the performance.
>> Especially if the xenstored gets slower when items are loaded.
> 
> Using signals won't work with qemu-dm in a stub domain.

Yes.  I have the following options in my mind to solve it.

1. Switch using signals for qemu-dm in Dom0, and xenstored for stub domains.
2. Prepare a dedicated event channel for saving QEMU state.

I guess using a dedicated event channel would be quicker than xenstored but 
slower than signals.  If it is, using a dedicated event channel for option 1 may 
be better.

Yoshi