![]() ![]() It's the job of the host operating system to distribute the execution threads of all currently running virtual machines over the physical hardware. The more virtual CPUs you configure, the more threads are started on the host. A guest CPU is just a thread running on the host computer. But there was no recent change how VirtualBox emulates multiple CPUs. The VirtualBox performance with multi-CPU guests needs improvement, this is a known problem. If needed, i can provide logs from host, and guests. I say connected, because it seems that only affects older host CPU's - running VM's on HP380 G7 (i7), with lagrer number of CPU on guest does not influence performance in a major way. I do also assume that this could be connected to other reports about suboptimal performance with more than one CPU. I did not manage to find anywhere any reference on how to make VirtualBox present CPU's as physical ones, so i do assume that this is something that needs to be done. On VMWare this was working flawlesly - you can go to VMWare knowelege base, and search for article 2030577. Increasing vCPU (guest CPU count) to anything above 2 causes huge performance degradation, and instability (frequent oopses). Host is installed using CentOS 6.5, as do guests.Īlso, HP580 G5 have 4 CPU's with 2x2 cores. It seems, that this is having some performance penalty, as guests seems to be running slower than before. Model name : Intel(R) Xeon(R) CPU X7350 2.93GHzįlags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc rep_good pni ssse3 lahf_lmĪddress sizes : 40 bits physical, 48 bits virtual When i did migrate those to VirtualBox, now CPU's are shown as "cores": ![]() Model name : Intel(R) Xeon(R) CPU X7542 2.67GHzįlags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts xtopology tsc_reliable nonstop_tsc aperfmperf pni ssse3 cx16 sse4_1 sse4_2 popcnt lahf_lm ida epb dtsĪddress sizes : 36 bits physical, 48 bits virtual In example - this is from guest running on another similar host with VMWare: All of them, when displaying cpuinfo, did show CPU's as separate physical packages. I have HP580 G5 machine, which was running ESXi package, and there was number of guest machines (mostly linuxes). But, it seems that it have more than one performance penalty. To enable ESXi nested virtualization use next command that added the vhv.allow parameter to the configuration file.The summary is somewhat missleading, sorry about that, but i was just not sure how to "commpress" it to something meaningfull.Īs up to 4.3.10 version, VirtualBox engine only support multiCPU configurations, where guest sees multiple CPU's as one physical CPU, with more cores and siblings.įor majority of use-cases this is sufficiant to emulate multi-cpu environment. In principle it works without those extensions too but with poor performance and it is not an option for productive environment (but maybe sufficient for some test cases). In nested virtualization, also the guest hypervisor should have access to hardware-assisted virtualization extensions, and that implies that the host hypervisor should expose those extension to its virtual machines. In order to have the fastest possible performance, near to native, any hypervisor should have access to some (real) hardware features that are generally useful for virtualization, the so called ‘hardware-assisted virtualization extensions’ (see ). enable businesses to deploy their own virtualization environment, e.g.test some dangerous/tricky procedure involving hypervisors before actually doing it on the real thing,.test (or learn) how to manage hypervisors before actual implementation,.This obviously adds an overhead to the nested environment, but it could be useful in some cases: In other words, you have a host hypervisor, hosting a guest hypervisor (as a vm), which can hosts its own vms. (which is of course running on another hypervisor) instead that on real hardware. ![]() Nested virtualization is when you run an hypervisor, like PVE or others, inside a virtual machine ![]()
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