From: Avi Kivity <avi@redhat.com>
To: Andreas Rittershofer <andreas@rittershofer.de>
Cc: kvm@vger.kernel.org
Subject: Re: CPU and RAM in VMs
Date: Sun, 12 Dec 2010 12:48:50 +0200 [thread overview]
Message-ID: <4D04A892.3090201@redhat.com> (raw)
In-Reply-To: <D3C60212-3D50-40B3-8C03-A077FFF04FD5@rittershofer.de>
On 12/12/2010 12:04 PM, Andreas Rittershofer wrote:
> Given is a situation as follows:
>
> One physical machine with 4 CPUs and 16 GB RAM. On this machine KVM and three virtual machines are installed.
>
> VM1: 2 CPUs, 8 GB RAM
> VM2: 2 CPUs, 6 GB RAM
> VM3: 1 CPU, 4 GB RAM
>
> As you can see, the sum of all virtual CPUs is greater than the number of physically available CPUs, the same with the RAM.
>
> What does happen, when all three VMs are started? They will need 5 CPUs, but only 4 CPUs are physically availabe, they will need 18 GB of RAM, but only 16 GB of RAM are physically available? What will KVM do in such a situation?
>
Linux will timeshare the cpus across the guests, and use swap space to
provide extra memory. Both of these can reduce performance.
--
error compiling committee.c: too many arguments to function
prev parent reply other threads:[~2010-12-12 10:48 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-12 10:04 CPU and RAM in VMs Andreas Rittershofer
2010-12-12 10:48 ` Avi Kivity [this message]
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