From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: [Qemu-devel] Ideas wiki for GSoC 2010
Date: Mon, 15 Mar 2010 08:23:45 -0500
Message-ID: <4B9E34E1.3090709@codemonkey.ws>
References: <20100310183023.6632aece@redhat.com> <4B9E2745.7060903@redhat.com> <20100315125313.GK9457@il.ibm.com> <20100315130310.GE13108@8bytes.org> <4B9E320E.7040605@redhat.com>
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Cc: Joerg Roedel <joro@8bytes.org>, Muli Ben-Yehuda <muli@il.ibm.com>,
	Luiz Capitulino <lcapitulino@redhat.com>,
	qemu-devel@nongnu.org, aliguori@us.ibm.com, kvm@vger.kernel.org,
	jan.kiszka@siemens.com, agraf@suse.de, agl@us.ibm.com,
	Nadav Amit <nadav.amit@gmail.com>,
	Ben-Ami Yassour1 <benami@il.ibm.com>
To: Avi Kivity <avi@redhat.com>
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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