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Message-ID: <5a4c169d-8e42-4609-87db-8b68f04bb0fe@linux.intel.com>
Date:   Tue, 24 Oct 2023 19:58:50 +0800
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Cc:     baolu.lu@linux.intel.com, jacob.jun.pan@linux.intel.com,
        kevin.tian@intel.com, yi.y.sun@intel.com, kvm@vger.kernel.org
Subject: Re: [PATCH 1/2] iommu: Introduce a rb_tree for looking up device
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To:     Huang Jiaqing <jiaqing.huang@intel.com>, joro@8bytes.org,
        will@kernel.org, robin.murphy@arm.com, dwmw2@infradead.org,
        linux-kernel@vger.kernel.org, iommu@lists.linux.dev
References: <20231024084124.11155-1-jiaqing.huang@intel.com>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <20231024084124.11155-1-jiaqing.huang@intel.com>
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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.

> 
> Signed-off-by: Huang Jiaqing <jiaqing.huang@intel.com>
> ---
>   drivers/iommu/io-pgfault.c | 104 ++++++++++++++++++++++++++++++++++++-
>   include/linux/iommu.h      |  16 ++++++
>   2 files changed, 118 insertions(+), 2 deletions(-)

Best regards,
baolu