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

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Message-ID: <5a4c169d-8e42-4609-87db-8b68f04bb0fe@linux.intel.com>
Date:   Tue, 24 Oct 2023 19:58:50 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Huang Jiaqing <jiaqing.huang@...el.com>, joro@...tes.org,
        will@...nel.org, robin.murphy@....com, dwmw2@...radead.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux.dev
Cc:     baolu.lu@...ux.intel.com, 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 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@...el.com>
> ---
>   drivers/iommu/io-pgfault.c | 104 ++++++++++++++++++++++++++++++++++++-
>   include/linux/iommu.h      |  16 ++++++
>   2 files changed, 118 insertions(+), 2 deletions(-)

Best regards,
baolu