I was wondering exactly the same. Why use Xen with HVM when you can use PV?
Originally Posted by evanjfraser
Also as someone already pointed out scenarios with 5-10-15 VM would be great in comparing Xen, KVM and Virtualbox.
Though improvement can be made in future, it's nice to see articles like this
XEn VGA PAssthru 95% baremetal at MS WOS
Thanks a lot, If I where a PC for hard gaming vendor I would sell Computers with this preinstalled config.
i only would change the GPUs for better performance of DX games and put Sabayon as Linux OS
This kind of tests are what i would like to read at Phoronix.
Originally Posted by Thanat0s
Xen HVM is actually faster than Xen PV for some workloads.. it really depends on the workload.
Originally Posted by tangram
(And vice versa; for some workloads Xen PV is faster than HVM).
If the workload consists of creating a lot of new processes (say, a kernel compile) then Xen HVM will be faster than Xen PV
(assuming you're of course running Xen PVHVM drivers in the HVM guest VM), because in Xen PV every new process creation
needs to be trapped by the hypervisor to check the pagetables for the new process. In Xen HVM guests you don't need to trap to the hypervisor to create new processes.
If the workload consists of "long running" processes, say, a mysql server, then Xen PV might be faster.
Where can I get the VM cfgfiles and hypervisor/system settings for this benchmark? I'd like to run some benchmarks myself with same settings.
The article doesn't state PVonHVM. It states HVM which ends up being a different beast. Also withh HVM you have emulation overhead.
But that sure would be an interesting article covering XEN PV, PVonHVM and HVM.
Xen PVHVM drivers are in upstream Linux kernel, so I believe they used PVHVM. If they didn't, then the benchmark is pointless, because they used VirtIO for KVM guests! (VirtIO is the PV driver for KVM).
Originally Posted by tangram
That would be the conclusion if this so called benchmark was run on the same hardware.
Originally Posted by M1kkko
It has already been pointed out that Xen has various options for virtualization. Benchmarks can be very helpful, particularly if they are setup to provide optimum performance. The exact setup must be documented.
I was surprised to see Xen tested with an Ubuntu HVM guest, and from the discussion here I gather that this guest wasn't even using PVHVM drivers.
+1 for tangram and pasik and others who pointed that out.
I had a second look at the benchmark and noticed that Xen was using ext4 partitions. IIRC the Xen wiki clearly states that Xen should be used with LVM for best disk I/O performance. Of course one would have to use the PVoHVM drivers to reach the full potential under HVM, and as already mentioned before, why not use a PV guest in the first place?
Running a benchmark where one contender is set up in a more or less optimal way (KVM with VirtIO driver) and the other (Xen) using what seems to be a low-performance setup is highly questionable. It hasn't been explained why HVM was chosen over PV (or why not using both options?), nor is it clear whether or not the PVoHVM drivers were used. It looks like most of the tests where Xen under-performs are disk I/O related.
Since I'm running a Xen system and I don't experience such performance issues, perhaps there is something wrong with the benchmark? For reference, my Windows 7 HVM guest achieves a Windows Experience Index (WEI) of 7.8 (of 7.9) for disk I/O using a SSD and GPLPV drivers. The driver itself helped improve the WEI by 1 index point.
The way it stands now, the conclusion of the benchmark is simply misleading.