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

Avi Kivity
2010-03-15T15:07:17Z

On 03/15/2010 03:23 PM, Anthony Liguori wrote:
> 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.

Do you know offhand of any unnecessary read/writes? There's
update_cr8_intercept(), but on normal exits, I don't see what else we
can remove.

--
error compiling committee.c: too many arguments to function