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Date: Mon, 15 Mar 2010 14:24:48 +0100
From: Joerg Roedel <joro@8bytes.org>
Subject: Re: [Qemu-devel] Ideas wiki for GSoC 2010
Message-ID: <20100315132448.GF13108@8bytes.org>
References: <20100310183023.6632aece@redhat.com> <4B9E2745.7060903@redhat.com>
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To: Avi Kivity <avi@redhat.com>
Cc: Muli Ben-Yehuda <muli@il.ibm.com>, agraf@suse.de, aliguori@us.ibm.com, kvm@vger.kernel.org, jan.kiszka@siemens.com, qemu-devel@nongnu.org, Luiz Capitulino <lcapitulino@redhat.com>, agl@us.ibm.com, Nadav Amit <nadav.amit@gmail.com>, Ben-Ami Yassour1 <benami@il.ibm.com>

On Mon, Mar 15, 2010 at 03:11:42PM +0200, 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.

Does it matter for the ept-on-ept case? The initial patchset of
nested-vmx implemented it and they reported a performance drop of around
12% between levels which is reasonable. So I expected the loss of
io-performance for l2 also reasonable in this case. My small measurement
was also done using npt-on-npt.

	Joerg