From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: [RFC][PATCH 12/13] Kemari: use signal to save qemu
	state for Kemari
Date: Wed, 18 Mar 2009 12:46:47 +0000
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To: Yoshiaki Tamura <tamura.yoshiaki@lab.ntt.co.jp>
Cc: "ospk-vm@lab.ntt.co.jp" <ospk-vm@lab.ntt.co.jp>, Ian Pratt <Ian.Pratt@eu.citrix.com>, xen-devel <xen-devel@lists.xensource.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Keir Fraser <Keir.Fraser@eu.citrix.com>
List-Id: xen-devel@lists.xenproject.org

Yoshiaki Tamura wrote:

> Stefano Stabellini wrote:
>> Ian Jackson wrote:
>>
>>> Stefano Stabellini writes ("Re: [Xen-devel] [RFC][PATCH 12/13] Kemari: use signal to save qemu state for Kemari"):
>>>> I did a couple of quick tests and it seems that signals are faster then
>>>> xenstore but still xenstore offers good performances.
>>>>
>>>> I measured the time using rdtsc at the sender size and at the receiver
>>>> size, the difference between the two values is the following:
>>>>
>>>> signals:   368836
>>>> xenstore: 1984632
>>> This is with an unloaded xenstored, I take it.
>>
>> Yes
> 
> 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 an event channel to notify qemu in a stubdom that a particular
event occurred improves things a lot: it is even faster than signals!

event channel: 20880

performances using an event channel with qemu as a process in dom0 are
about the same.