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Subject: Re: [PATCH Kernel v22 0/8] Add UAPIs to support migration for VFIO
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To:     Alex Williamson <alex.williamson@redhat.com>,
        "Dr. David Alan Gilbert" <dgilbert@redhat.com>
CC:     Yan Zhao <yan.y.zhao@intel.com>, <cjia@nvidia.com>,
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From:   Kirti Wankhede <kwankhede@nvidia.com>
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On 5/29/2020 4:29 AM, Alex Williamson wrote:
> On Wed, 27 May 2020 09:48:22 +0100
> "Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:
>> * Yan Zhao (yan.y.zhao@intel.com) wrote:
>>> BTW, for viommu, the downtime data is as below. under the same network
>>> condition and guest memory size, and no running dirty data/memory produced
>>> by device.
>>> (1) viommu off
>>> single-round dirty query: downtime ~100ms
>>
>> Fine.
>>
>>> (2) viommu on
>>> single-round dirty query: downtime 58s
>>
>> Youch.
> 
> Double Youch!  But we believe this is because we're getting the dirty
> bitmap one IOMMU leaf page at a time, right?  We've enable the kernel
> to get a dirty bitmap across multiple mappings, but QEMU isn't yet
> taking advantage of it.  Do I have this correct?  Thanks,
> 

That's correct.

Thanks,
Kirti