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


From: Avi Kivity
Subject: Re: [Qemu-devel] Ideas wiki for GSoC 2010
Date: Mon, 15 Mar 2010 17:06:57 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100301 Fedora/3.0.3-1.fc12 Thunderbird/3.0.3

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





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