linux-kernel - Re: [PATCH] iommu/vt-d: Introduce a rb

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Date:   Mon, 21 Aug 2023 13:52:01 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Huang Jiaqing <jiaqing.huang@...el.com>
Cc:     kvm@...r.kernel.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, joro@...tes.org, will@...nel.org,
        robin.murphy@....com, kevin.tian@...el.com,
        baolu.lu@...ux.intel.com, jacob.jun.pan@...ux.intel.com,
        yi.l.liu@...el.com, yi.y.sun@...el.com
Subject: Re: [PATCH] iommu/vt-d: Introduce a rb_tree for looking up device

On Mon, Aug 21, 2023 at 12:16:59AM -0700, Huang Jiaqing wrote:
> The existing IO page fault handler locates the PCI device by calling
> pci_get_domain_bus_and_slot(), which searches the list of all PCI
> devices until the desired PCI device is found. This is inefficient
> because the algorithm efficiency of searching a list is O(n). In the
> critical path of handling an IO page fault, this can cause a significant
> performance bottleneck.
> 
> To improve the performance of the IO page fault handler, replace
> pci_get_domain_bus_and_slot() with a local red-black tree. A red-black
> tree is a self-balancing binary search tree, which means that the
> average time complexity of searching a red-black tree is O(log(n)). This
> is significantly faster than O(n), so it can significantly improve the
> performance of the IO page fault handler.
> 
> In addition, we can only insert the affected devices (those that have IO
> page fault enabled) into the red-black tree. This can further improve
> the performance of the IO page fault handler.
> 
> Signed-off-by: Huang Jiaqing <jiaqing.huang@...el.com>
> ---
>  drivers/iommu/intel/iommu.c | 68 +++++++++++++++++++++++++++++++++++++
>  drivers/iommu/intel/iommu.h |  8 +++++
>  drivers/iommu/intel/svm.c   | 13 +++----
>  3 files changed, 81 insertions(+), 8 deletions(-)

I feel like this should be a helper library provided by the core
code, doesn't every PRI driver basically need the same thing?

Jason