justin randell <[email protected]> writes:
> On 1 November 2010 09:16, Daniel Pittman <[email protected]> wrote:
>>
>>>> Are there different types or levels of hardware virtualization available
>>>> off the shelf, or it is one-size-fits-all?
>>>
>>> Well there’s Intel VT-x and there’s AMD-V, which are the duopoly’s
>>> equivalents. Both are supported by VirtualBox, VMware, KVM, etc.
>>>
>>> Personally, I think that if you buy a new PC with hardware virtualisation,
>>> the performance benefit you will see will be coming from the faster hardware
>>> more than the VT-x/AMD-V support.
>>
>> *nod* Also, keep in mind that one of the biggest factors in VM performance
>> is
>> going to be I/O for most users.
>>
>> That means that the performance of your paravirtualized devices is the key
>> for
>> getting better performance - and that usually just means picking a VM
>> solution
>> with appropriate "guest" drivers and all.
>>
>> (Unless you plan on mapping physical hardware into the VM, in which case VT-d
>> or the AMD equivalent makes a difference.)
>
> yep, I/O is normally a killer. at work, all dev machines have (at least) two
> physical drives, so VMs can be given a disc separate from the host OS. we
> find that's the simplest, best bang-for-buck way to get good VM performance.
Only if you have PV disk drivers - performance with the emulated hardware,
even SAS and SCSI controllers, is generally way lower than the PV stuff
because of the overheads of emulation.[1]
FWIW, using KVM we reproduced the widely reported "native performance" using
direct I/O and an LVM slice results; those later should work for any raw block
device, not just LVM. (Which matches your comment, of course. :)
Daniel
Footnotes:
[1] Really good non-PV drivers and good hardware can reduce it to the
equivalent of only a few transitions into kernel mode, but they can't be
as efficient as the "one or less" that PV drivers manage.
--
✣ Daniel Pittman ✉ [email protected] ☎ +61 401 155 707
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