On Tue, Mar 15, 2016 at 10:49:14PM +0000, Gordan Bobic wrote: > On 2016-03-15 22:12, Richard W.M. Jones wrote: > >On Tue, Mar 15, 2016 at 07:49:22PM +0000, Gordan Bobic wrote: > >>On 2016-03-15 18:32, Richard W.M. Jones wrote: > >>>I may be missing some context here, but is there some reason not to > >>>just use a VM? > >> > >>Performance for one. > > > >Can you precisely quantify that? > > On ARM? No, haven't tried it yet. On x86-64? Between 30% and 40% > on a concurrent load saturating the CPU. Measured with different > hypervisors (KVM, Xen and ESXi) and different generations of > Intel CPUs from Core2 to Westmere Xeons. The results are reproducible > on different loads, from a simple parallel kernel compile to a > parallel read-only replay of MySQL general log. You must be doing something very wrong if you see such a huge slowdown with KVM. Red Hat has a team that tracks performance and looks for regressions between releases. You shouldn't see more than a 5% slowdown, except in rare and exceptional corner cases, or if it's configured wrong. Hard to say what - perhaps not using virtio, or not using the right <cpu> model, or maybe overprovisioning. > Here are some old results on Core2 class hardware: > https://www.altechnative.net/2012/08/04/virtual-performance-part-1-vmware/ I can't comment on VMware, nor on results from 4 years ago. > Unfortunately, later version of both hypervisors and hardware > (I last ran similar tests using MySQL last year), exhibit the > exact same performance degradation. > > To reproduce: > 1) 1 host, 1 VM > 2) Give the VM all CPU cores available on the host > 3) Run test with double the number of threads as there are CPU cores So the problem is overprovisioning. > >I think RHELSA 7.3 will have a 4.5 kernel. Of course "LT" kernels > >aren't really relevant for Red Hat, because we spend huge amounts of > >money supporting our kernels long term. > > Let's not go there: > https://bugzilla.redhat.com/show_bug.cgi?id=773107 We don't support self-compiled kernels, for fairly obvious reasons. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v