linux-kernel - Re: [PATCH 1/2] iommu: Introduce a rb

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Date:   Fri, 27 Oct 2023 14:09:11 +0800
From:   "Huang, Jiaqing" <jiaqing.huang@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>, joro@...tes.org,
        will@...nel.org, robin.murphy@....com, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev
Cc:     jacob.jun.pan@...ux.intel.com, kevin.tian@...el.com,
        yi.y.sun@...el.com, kvm@...r.kernel.org
Subject: Re: [PATCH 1/2] iommu: Introduce a rb_tree for looking up device

On 10/24/2023 7:58 PM, Baolu Lu wrote:

> On 2023/10/24 16:41, 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 is not performance
>> friendly given that I/O page fault handling patch is performance
>> critical, and parallel heavy dsa_test may cause cpu stuck due to
>> the low efficiency and lock competition in current path.
>>
>> 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.
>>
>> This series depends on "deliver page faults to user space" patch-set:
>> https://lore.kernel.org/linux-iommu/20230928042734.16134-1-baolu.lu@linux.intel.com/
>>
>
> The note above is not part of the commit message, and should be placed
> below the tear line or in the cover letter, if there is one.

Will fix, thanks for catching!

BRs,
Jiaqing