> KVM performance is very poor?
>
> I have tested a simple IO/CPU mixture testcase under both RHEL5/Xen and
> RHEL6/KVM guest.

> Under the naked machine, both RHEL5 and RHEL6 can get 250M/s,
> XEN guest can get 240M/s
> KVM guest can get only 120M/s

>   Regards
>   Kirby Zhou

Do not know the KVM version you tested against. But on RHEL 5 there was a
performance hitting bug

https://rhn.redhat.com/errata/RHBA-2010-0536.html

* the virtio-blk back end for qemu-kvm performed unnecessary zeroing of
memory on every I/O request, which reduced virtual guest performance. With
this update,t he virtio-blk back end avoids spurious zeroing of request
structures on each I/O request, with the result that guest performance is
increased. (BZ#604159)

Alexander



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