Re: [Qemu-devel] Ideas wiki for GSoC 2010

Anthony Liguori
2010-03-15T13:23:49Z

On 03/15/2010 08:11 AM, Avi Kivity wrote:
> On 03/15/2010 03:03 PM, Joerg Roedel wrote:
>>
>>>> I will add another project - iommu emulation. Could be very useful
>>>> for doing device assignment to nested guests, which could make
>>>> testing a lot easier.
>>> Our experiments show that nested device assignment is pretty much
>>> required for I/O performance in nested scenarios.
>> Really? I did a small test with virtio-blk in a nested guest (disk read
>> with dd, so not a real benchmark) and got a reasonable read-performance
>> of around 25MB/s from the disk in the l2-guest.
>>
>
> Your guest wasn't doing a zillion VMREADs and VMWRITEs every exit.
>
> I plan to reduce VMREAD/VMWRITE overhead for kvm, but not much we can
> do for other guests.

VMREAD/VMWRITEs are generally optimized by hypervisors as they tend to
be costly. KVM is a bit unusual in terms of how many times the
instructions are executed per exit.

Regards,

Anthony Liguori