On 2020/12/9 19:54, Cornelia Huck wrote:
> On Tue, 8 Dec 2020 21:55:53 +0800
> "xuxiaoyang (C)" <xuxiaoyang2@xxxxxxxxxx> wrote:
>
>> On 2020/11/21 15:58, xuxiaoyang (C) wrote:
>>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>>> each to return the physical pfn. When dealing with large arrays of
>>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>>> it is processed page by page.In this case, we can divide the iova pfn
>>> array into multiple continuous ranges and optimize them. For example,
>>> when the iova pfn array is {1,5,6,7,9}, it will be divided into three
>>> groups {1}, {5,6,7}, {9} for processing. When processing {5,6,7}, the
>>> number of calls to pin_user_pages_remote is reduced from 3 times to once.
>>> For single page or large array of discontinuous iovas, we still use
>>> vfio_pin_page_external to deal with it to reduce the performance loss
>>> caused by refactoring.
>>>
>>> Signed-off-by: Xiaoyang Xu <xuxiaoyang2@xxxxxxxxxx>
>
> (...)
>
>>
>> hi Cornelia Huck, Eric Farman, Zhenyu Wang, Zhi Wang
>>
>> vfio_pin_pages() accepts an array of unrelated iova pfns and processes
>> each to return the physical pfn. When dealing with large arrays of
>> contiguous iovas, vfio_iommu_type1_pin_pages is very inefficient because
>> it is processed page by page. In this case, we can divide the iova pfn
>> array into multiple continuous ranges and optimize them. I have a set
>> of performance test data for reference.
>>
>> The patch was not applied
>> 1 page 512 pages
>> no huge pages： 1638ns 223651ns
>> THP： 1668ns 222330ns
>> HugeTLB： 1526ns 208151ns
>>
>> The patch was applied
>> 1 page 512 pages
>> no huge pages 1735ns 167286ns
>> THP： 1934ns 126900ns
>> HugeTLB： 1713ns 102188ns
>>
>> As Alex Williamson said, this patch lacks proof that it works in the
>> real world. I think you will have some valuable opinions.
>
> Looking at this from the vfio-ccw angle, I'm not sure how much this
> would buy us, as we deal with IDAWs, which are designed so that they
> can be non-contiguous. I guess this depends a lot on what the guest
> does.
>
> Eric, any opinion? Do you maybe also happen to have a test setup that
> mimics workloads actually seen in the real world?
>
> .
>
Thank you for your reply. The iova array constructed using
pfn_array_alloc is continuous, and I think there will be
some performance improvements here.
Regards,
Xu
