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

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Message-ID: <fe03b53a-c9f9-cc6b-a1fd-d6fd2f1a1ddc@linux.intel.com>
Date:   Tue, 22 Aug 2023 15:32:26 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...pe.ca>,
        Huang Jiaqing <jiaqing.huang@...el.com>
Cc:     baolu.lu@...ux.intel.com, 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, 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 2023/8/22 0:52, Jason Gunthorpe wrote:
> 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?

It seems to be. pci_get_domain_bus_and_slot() is also used in the amd
driver. And the risc-v iommu driver under discussion is also proposing
this.

Best regards,
baolu