[CentOS-virt] What are KVM guest cores?
Hi All, What are guest cores in KVM? Are they fake, like everything else in the guest? Just another process running on the host emulating a core? Or are the guest cores actually connected directly to the physical cores on my motherboard? Many thanks, -T ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
Re: [CentOS-virt] SPICE Benchmark
On Wed, Nov 17, 2010 at 10:02:49PM -0500, Scott Dowdle wrote: Greetings, - Original Message - So as I understand it correctly, this whole SPICE thing is just something like VNC on steroids? Why can't we have this SPICE thing work on physical hosts as well? SPICE was specifically designed to be a display protocol for a KVM virtual machine. Most remote display protocols have two pieces... a client and a server. SPICE has three... a client, a server, and a qxl device driver provided inside of a KVM virtual machine. It is probably possible to take the SPICE protocol and adapt it to work without the qxl device driver... but no one has done that yet. The best experience I've seen for a remote Linux box was provided by No Machine's NX protocol. FreeNX comes from NX but it appears FreeNX has stalled. Google created some project, I forget the name, forked from FreeNX I believe. No Machine is working on version 4.0 of NX and supposedly will be releasing a beta in the not too distant future. Some time ago they posted a lot of information about NX 4.0 on their website and it seems to rival SPICE to a certain degree... but that remains to be seen. Google's NX implementation is called 'neatx': http://code.google.com/p/neatx/ What I'd like to see happen would be for SPICE to be adapted to a general purpose remote display protocol or perhap Red Hat could buy No Machine and open source that protocol too. :) NX the protocol is open already.. :) Nomachine's NX server product is not.. -- Pasi ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
[CentOS-virt] [HOWTO] Running Xen 4.0 host (dom0) with Redhat Enterprise Linux 6 (RHEL6)
Hello, If you're interested in running Xen 4.0 hypervisor/dom0 on RHEL6, take a look at here: http://wiki.xen.org/xenwiki/RHEL6Xen4Tutorial It explains steps needed to rebuild Xen 4.0.1 src.rpm from Fedora on RHEL6, and how to fetch dom0 capable 2.6.32.x kernel from upstream git repository. It also shows how to get libvirt/virt-manager working with Xen on RHEL6. Hopefully it helps :) -- Pasi ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
Re: [CentOS-virt] [HOWTO] Running Xen 4.0 host (dom0) with Redhat Enterprise Linux 6 (RHEL6)
2010/11/18 Pasi Kärkkäinen pa...@iki.fi: Hello, If you're interested in running Xen 4.0 hypervisor/dom0 on RHEL6, take a look at here: http://wiki.xen.org/xenwiki/RHEL6Xen4Tutorial It explains steps needed to rebuild Xen 4.0.1 src.rpm from Fedora on RHEL6, and how to fetch dom0 capable 2.6.32.x kernel from upstream git repository. It also shows how to get libvirt/virt-manager working with Xen on RHEL6. Hopefully it helps :) Very nice, thanks! I'll test it when time permits, but for now I'll enjoy the working-out-of-the-box experience I get with KVM on RHEL ;) Best regards Kenni ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
[CentOS-virt] what scheduling algorithm does KVM use?
This may not be the best place to ask, but I was prompted by a question about guest cores on KVM. We currently use VMWare Server (v1.0) on CentOS5. It supports up to two virtual CPUs, but not very well, as I understand it. VMWare Server 2.0 might do better at supporting the same maximum of 2 CPUs, but if my research is correct, they both use what is called strict co-scheduling. Which means, if a two virtual-CPU VM is waiting for a time slice on the physical host, there needs to be two physical CPUs available to be allocated. This is because amount of time scheduled to each virtual CPU has to stay equal, else assumptions in the virtualised software may become false and things start going wrong. The problem with this is that it is obviously more of a constraint to have two physical CPUs available. Therefore adding virtual CPUs to a co-scheduled VM can actually make performance worse if the physical CPUs are under any sort of contention. Performance degrades rapidly under load - which is exactly what you don't want for a webserver. Therefore advice seems to be to avoid using multi-virtual CPU VMs. [1] VMWare ESX uses something supposedly better, called relaxed co-scheduling. [2]. We're not likely to use that any time soon, since we are using 11 root servers running CentOS. I did try and research the algorithm(s) used by KVM. Apparently it doesn't use co-scheduling, but possibly something called the completely fair scheduler, but I'm no an expert in VM scheduling and I didn't manage to discover what this means, nor specifically what the implications are for performance were in terms of scaling up the number of virtual CPUs on KVM. (I understand that the number of virtual CPUs supported by KVM is be quite high.) Anyway, I've been asked how to scale a VM up utilise more - say four or more - physical CPUs. Is KVM better at this than VMware Server, or does the same basic problem persist? Thanks, Nick 1. http://communities.vmware.com/thread/169323 http://cs.gmu.edu/~hfoxwell/cs671projects/southern_v12n.pdf The SMP scheduling algorithms used by ESX server and by Xen have a low overhead for single-threaded compute inten- sive workloads. However, they do not scale as well for multi-threaded workloads on a system with overcommit- ted CPU resources. 2. http://communities.vmware.com/thread/157849 http://communities.vmware.com/docs/DOC-4960 http://communities.vmware.com/docs/DOC-5501 ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
Re: [CentOS-virt] what scheduling algorithm does KVM use?
2010/11/19 Nick oinksoc...@letterboxes.org: The problem with this is that it is obviously more of a constraint to have two physical CPUs available. Therefore adding virtual CPUs to a co-scheduled VM can actually make performance worse if the physical CPUs are under any sort of contention. Performance degrades rapidly under load - which is exactly what you don't want for a webserver. Therefore advice seems to be to avoid using multi-virtual CPU VMs. [1] As long as you keep the number of CPUs for *each* VM - equal to or lower than - the number of physical cores, your performance should not suffer with KVM. If you assign more CPUs to one VM than you have available cores (a core can also be a hyperthreaded core), you will for sure run into performance problems. I did try and research the algorithm(s) used by KVM. Apparently it doesn't use co-scheduling, but possibly something called the completely fair scheduler, The good thing about KVM compared to other virtualization solutions, is that KVM doesn't try to reinvent the wheel. It leaves scheduling to the Linux kernel, so whatever your Linux system is setup to use, KVM will use that. You can choose to run CFS (Completely Fair Scheduler), deadline, BFS, or whatever scheduler you prefer. As long as Linux uses it, KVM will use it. but I'm no an expert in VM scheduling and I didn't manage to discover what this means, nor specifically what the implications are for performance were in terms of scaling up the number of virtual CPUs on KVM. (I understand that the number of virtual CPUs supported by KVM is be quite high.) If you want a really competent answer to your question, send it to the kvm-devel list...they don't mind user questions like this, and as long as you're asking a relevant question, there's a good chance of getting a highly competent answer :) Best regards Kenni ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
Re: [CentOS-virt] SPICE Benchmark
Greetings, - Original Message - Google's NX implementation is called 'neatx': http://code.google.com/p/neatx/ Thanks. I was looking for that. NX the protocol is open already.. :) It is for all versions before 4.0. 4.0 will be completely closed. TYL, -- Scott Dowdle 704 Church Street Belgrade, MT 59714 (406)388-0827 [home] (406)994-3931 [work] ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
Re: [CentOS-virt] what scheduling algorithm does KVM use?
Thanks for the quick reply. On 18/11/10 23:45, Kenni Lund wrote: The good thing about KVM compared to other virtualization solutions, is that KVM doesn't try to reinvent the wheel. It leaves scheduling to the Linux kernel, so whatever your Linux system is setup to use, KVM will use that. You can choose to run CFS (Completely Fair Scheduler), deadline, BFS, or whatever scheduler you prefer. As long as Linux uses it, KVM will use it. Is this process scheduling we're talking about here? Hmm, and I wonder how I find out what scheduling algorithm my kernel is using. So, this sounds feasible... except if virtual CPUs must have time shared equally as the VMWare co-scheduling explanations imply. A scheduler for threads / processes presumably wouldn't guarantee such a thing? Maybe I'll go and investigate the KVM list Thanks N ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
Re: [CentOS-virt] What are KVM guest cores?
Do you have a rule of thumb as to how many core to assign to a guest? For instance, with an Intel x5650 with 6 real and 12 hyperthreaded cores, how many cores would you assign to the guest? It fully depends on the load of your guests and how many guests you want/need to run on a single server. You need to perform some testing to know what will work the best in your case. One thing to remember though: In your case, if you create two guests with 12 virtual CPUs each, and one of them crashes and take all its 12 virtual CPUs up to 100%, it will essentially take most of the processing power away from the second guest, leaving the second guest in a close-to-useless state (depending on your scheduler, but you get the point). If you on the other hand had assigned 6 cores to each of them, the second guest would have remained unaffected, since it just uses the 6 cores with no load. So if your guest will not utilize the extra CPUs anyway, then don't assign them. Best regards Kenni ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
Re: [CentOS-virt] what scheduling algorithm does KVM use?
2010/11/19 Nick oinksoc...@letterboxes.org: Thanks for the quick reply. On 18/11/10 23:45, Kenni Lund wrote: The good thing about KVM compared to other virtualization solutions, is that KVM doesn't try to reinvent the wheel. It leaves scheduling to the Linux kernel, so whatever your Linux system is setup to use, KVM will use that. You can choose to run CFS (Completely Fair Scheduler), deadline, BFS, or whatever scheduler you prefer. As long as Linux uses it, KVM will use it. Is this process scheduling we're talking about here? Yep, a virtual CPU is just a process on the host Linux system. So, this sounds feasible... except if virtual CPUs must have time shared equally as the VMWare co-scheduling explanations imply. A scheduler for threads / processes presumably wouldn't guarantee such a thing? I think cgroups is the solution, if you want to guarantee resources to some guests. I haven't tested it with KVM, but perhaps nice and ionice can be useful as well...the guests are just Linux processes after all. Maybe I'll go and investigate the KVM list :) Best regards Kenni ___ CentOS-virt mailing list CentOS-virt@centos.org http://lists.centos.org/mailman/listinfo/centos-virt
