Re: How many threads should a kvm vm be starting?
On September 28, 2011, Daniel P. Berrange wrote: > On Tue, Sep 27, 2011 at 04:04:41PM -0600, Thomas Fjellstrom wrote: > > On September 27, 2011, Avi Kivity wrote: > > > On 09/27/2011 03:29 AM, Thomas Fjellstrom wrote: > > > > I just noticed something interesting, a virtual machine on one of my > > > > servers seems to have 69 threads (including the main thread). Other > > > > guests on the machine only have a couple threads. > > > > > > > > Is this normal? or has something gone horribly wrong? > > > > > > It's normal if the guest does a lot of I/O. The thread count should go > > > down when the guest idles. > > > > Ah, that would make sense. Though it kind of defeats assigning a vm a > > single cpu/core. A single VM can now DOS an entire multi-core-cpu > > server. It pretty much pegged my dual core (with HT) server for a couple > > hours. > > You can mitigate these problems by putting each KVM process in its own > cgroup, and using the 'cpu_shares' tunable to ensure that each KVM > process gets the same relative ratio of CPU time, regardless of how > many threads it is running. With newer kernels there are other CPU > tunables for placing hard caps on CPU utilization of the process as > a whole too. I'll have to look into how to set that up with libvirt. A brief search leads me to believe its rather easy to set up, so I'll have to do that asap :) > Regards, > Daniel -- Thomas Fjellstrom tho...@fjellstrom.ca -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: How many threads should a kvm vm be starting?
On Tue, Sep 27, 2011 at 04:04:41PM -0600, Thomas Fjellstrom wrote: > On September 27, 2011, Avi Kivity wrote: > > On 09/27/2011 03:29 AM, Thomas Fjellstrom wrote: > > > I just noticed something interesting, a virtual machine on one of my > > > servers seems to have 69 threads (including the main thread). Other > > > guests on the machine only have a couple threads. > > > > > > Is this normal? or has something gone horribly wrong? > > > > It's normal if the guest does a lot of I/O. The thread count should go > > down when the guest idles. > > Ah, that would make sense. Though it kind of defeats assigning a vm a single > cpu/core. A single VM can now DOS an entire multi-core-cpu server. It pretty > much pegged my dual core (with HT) server for a couple hours. You can mitigate these problems by putting each KVM process in its own cgroup, and using the 'cpu_shares' tunable to ensure that each KVM process gets the same relative ratio of CPU time, regardless of how many threads it is running. With newer kernels there are other CPU tunables for placing hard caps on CPU utilization of the process as a whole too. Regards, Daniel -- |: http://berrange.com -o-http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: How many threads should a kvm vm be starting?
On September 27, 2011, Avi Kivity wrote: > On 09/27/2011 03:29 AM, Thomas Fjellstrom wrote: > > I just noticed something interesting, a virtual machine on one of my > > servers seems to have 69 threads (including the main thread). Other > > guests on the machine only have a couple threads. > > > > Is this normal? or has something gone horribly wrong? > > It's normal if the guest does a lot of I/O. The thread count should go > down when the guest idles. Ah, that would make sense. Though it kind of defeats assigning a vm a single cpu/core. A single VM can now DOS an entire multi-core-cpu server. It pretty much pegged my dual core (with HT) server for a couple hours. -- Thomas Fjellstrom tho...@fjellstrom.ca -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: How many threads should a kvm vm be starting?
On 09/27/2011 03:29 AM, Thomas Fjellstrom wrote: I just noticed something interesting, a virtual machine on one of my servers seems to have 69 threads (including the main thread). Other guests on the machine only have a couple threads. Is this normal? or has something gone horribly wrong? It's normal if the guest does a lot of I/O. The thread count should go down when the guest idles. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
How many threads should a kvm vm be starting?
I just noticed something interesting, a virtual machine on one of my servers seems to have 69 threads (including the main thread). Other guests on the machine only have a couple threads. Is this normal? or has something gone horribly wrong? -- Thomas Fjellstrom tho...@fjellstrom.ca -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
