From: Cornelia Huck <cohuck@redhat.com>
To: "xuxiaoyang (C)" <xuxiaoyang2@huawei.com>,
Eric Farman <farman@linux.ibm.com>
Cc: <linux-kernel@vger.kernel.org>, <kvm@vger.kernel.org>,
Alex Williamson <alex.williamson@redhat.com>,
<kwankhede@nvidia.com>, <wu.wubin@huawei.com>,
<maoming.maoming@huawei.com>, <xieyingtai@huawei.com>,
<lizhengui@huawei.com>, <wubinfeng@huawei.com>,
Zhenyu Wang <zhenyuw@linux.intel.com>,
Zhi Wang <zhi.a.wang@intel.com>
Subject: Re: [PATCH v2] vfio iommu type1: Improve vfio_iommu_type1_pin_pages performance
Date: Wed, 9 Dec 2020 12:54:50 +0100 [thread overview]
Message-ID: <20201209125450.3f5834ab.cohuck@redhat.com> (raw)
In-Reply-To: <4d58b74d-72bb-6473-9523-aeaa392a470e@huawei.com>
On Tue, 8 Dec 2020 21:55:53 +0800
"xuxiaoyang (C)" <xuxiaoyang2@huawei.com> 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@huawei.com>
(...)
>
> 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?
next prev parent reply other threads:[~2020-12-09 11:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-21 7:58 [PATCH v2] vfio iommu type1: Improve vfio_iommu_type1_pin_pages performance xuxiaoyang (C)
2020-12-08 13:55 ` xuxiaoyang (C)
2020-12-09 11:54 ` Cornelia Huck [this message]
2020-12-09 14:42 ` Eric Farman
2020-12-10 13:56 ` xuxiaoyang (C)
2020-12-14 18:58 ` Eric Farman
2020-12-15 13:13 ` xuxiaoyang (C)
2020-12-10 13:54 ` xuxiaoyang (C)
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