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

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] VM start time slows with large number of VMs
From: "Daniel P. Berrange" <berrange@xxxxxxxxxx>
Date: Wed, 5 Sep 2007 18:37:32 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, "Carb, Brian A" <Brian.Carb@xxxxxxxxxx>
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On Wed, Sep 05, 2007 at 06:11:06PM +0100, Keir Fraser wrote:
> xenstore slowness seems a reasonable hypothesis. How does performance of
> ?time 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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