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 <[email protected]>
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