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RE: [Xen-devel] VM start time slows with large number of VMs

To: "Daniel P. Berrange" <berrange@xxxxxxxxxx>, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: RE: [Xen-devel] VM start time slows with large number of VMs
From: "Carb, Brian A" <Brian.Carb@xxxxxxxxxx>
Date: Mon, 24 Sep 2007 09:18:41 -0500
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References: <089B0D75973E1241B941D0A9854F23FC08E17469@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> <C304A1BA.D3AD%Keir.Fraser@xxxxxxxxxxxx> <20070905173732.GH5503@xxxxxxxxxx>
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Thread-topic: [Xen-devel] VM start time slows with large number of VMs
We compared total elapsed time to start 320 para VMs on ES7000 (56x 160gb) 
where xenstore was on physical disk vs ram disk:

physical:  5 hours 19 minutes
ram disk:  4 hours  2 minutes

brian carb
unisys corporation - malvern, pa

-----Original Message-----
From: Daniel P. Berrange [mailto:berrange@xxxxxxxxxx] 
Sent: Wednesday, September 05, 2007 1:38 PM
To: Keir Fraser
Cc: Carb, Brian A; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] VM start time slows with large number of VMs

On Wed, Sep 05, 2007 at 06:11:06PM +0100, Keir Fraser wrote:
> xenstore slowness seems a reasonable hypothesis. How does performance 
> of Œtime xenstore-ls >/dev/null¹ change as you increase the number of guests?

There's another issue with the way hotplug scripts do locking which exhbits 
fairly pathelogical behaviour when a large number of guests are started 
concurrently. We've got a patch we're evaluating which changes  the use of lock 
files + looping + sleeps, to instead use the 'flock' shell util.

I suspect the performance issues will be a combination of both the locking 
stuff and the xenstore I/O. You might also want to try putting 
/var/lib/xenstored onto tmpfs eg in  initscripts before xenstored starts ...

  mkdir /dev/shm/xenstored
  mount --bind /dev/shm/xenstored /var/lib/xenstored

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