Native Linux KVM tool v2

Posted Jun 16, 2011 22:41 UTC (Thu) by aliguori (subscriber, #30636)
In reply to: Native Linux KVM tool v2 by bronson
Parent article: Native Linux KVM tool v2

The mode the they are using is not the default in QEMU because it's faster than bare metal assuming an otherwise uncontended system with plenty of memory to burn. The results are inconsistent and the safety of doing this depends on how well behaved your guest is.

It's usually not what people want to use even if it makes for artificially high benchmarks.

Native Linux KVM tool v2

Posted Jun 17, 2011 11:41 UTC (Fri) by Darkmere (subscriber, #53695) [Link] (1 responses)

Frankly, even when using virt-install I'm never certain if it's the right speed or not. Mostly _io_ tends to send systems into 20+ load "wait until world peace happens" even with (supposedly?) virtio enabled.

the current state of qemu-kvm is at times, a headache to deal with.

Speeding up qemu-kvm

Posted Jun 17, 2011 22:04 UTC (Fri) by jrn (subscriber, #64214) [Link]

Based on

> Some block drivers perform badly with cache=writethrough, most notably, qcow2. If performance is more important than correctness, cache=writeback should be used with qcow2.

I switched to cache=unsafe, and life became way better. The kind of tests I do in VMs let me recreate the image if there's a sudden crash, so safety is not such a worry. Not sure if virt-install does something like that.