Re: [PATCH] iommu/vt-d: Introduce a rb_tree for looking up device

[Baolu Lu]

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@xxxxxxxxx>
> > ---
> >   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