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Message-ID: <bf2dbc64-a6b6-4763-b497-80f0f1675366@intel.com>
Date:   Fri, 27 Oct 2023 14:09:11 +0800
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Subject: Re: [PATCH 1/2] iommu: Introduce a rb_tree for looking up device
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To:     Baolu Lu <baolu.lu@linux.intel.com>, joro@8bytes.org,
        will@kernel.org, robin.murphy@arm.com, dwmw2@infradead.org,
        linux-kernel@vger.kernel.org, iommu@lists.linux.dev
Cc:     jacob.jun.pan@linux.intel.com, kevin.tian@intel.com,
        yi.y.sun@intel.com, kvm@vger.kernel.org
References: <20231024084124.11155-1-jiaqing.huang@intel.com>
 <5a4c169d-8e42-4609-87db-8b68f04bb0fe@linux.intel.com>
From:   "Huang, Jiaqing" <jiaqing.huang@intel.com>
In-Reply-To: <5a4c169d-8e42-4609-87db-8b68f04bb0fe@linux.intel.com>
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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