On Wed, Oct 14, 2015 at 04:20:13PM +1100, Russell Coker wrote:
The last time I tried KVM on my laptop the performance was a lot slower than native performance as opposed to Xen which was near enough to native hardware performance that the difference didn't matter. I've never even tested KVM on a server because the performance on my laptop (admittedly a couple of years ago) was very disappointing. Last time I tested KVM performance was not only noticably worse (EG compiles of selinux-policy-default taking about 50% longer) but the increase in CPU use was an issue of cooling.
Has KVM improved a lot recently?
According to the man page for the /usr/bin/kvm wrapper script, it no longer falls back to emulation mode if kvm support is unavailable. `man kvm` says: The script executes qemu-system-x86_64 -enable-kvm passing all other command-line arguments to the qemu binary. This is not the same as old kvm binary, which was using less strict construct, similar to qemu-system-x86_64 -machine accel=kvm:tcg New wrapper ensures that kvm mode is enabled, or the VM will not start, while old code falled back to emulation (tcg) mode if kvm isn't avail- able. if your laptop didn't have kvm properly installed and configured (or your CPU didn't have virtualisation extensions), then it would have fallen back to slow emulation mode.
How can anything be so much better than Xen when Xen has been so close to native performance for so long?
personally, i've never noticed any significant difference between kvm and xen performance...at least, not on modern virtualisation-enabled CPUs. craig -- craig sanders <cas@taz.net.au>