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

["Carb, Brian A" <Brian.Carb@xxxxxxxxxx>]

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


Dan.
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