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When vfio_pin_pages_remote() is called with a range of addresses that includes large folios, the function currently performs individual statistics counting operations for each page. This can lead to significant performance overheads, especially when dealing with large ranges of pages. Batch processing of statistical counting operations can effectively enhance performance. In addition, the pages obtained through longterm GUP are neither invalid nor reserved. Therefore, we can reduce the overhead associated with some calls to function is_invalid_reserved_pfn(). The performance test results for completing the 16G VFIO IOMMU DMA mapping are as follows. Base(v6.16): ------- AVERAGE (MADV_HUGEPAGE) -------- VFIO MAP DMA in 0.049 s (328.5 GB/s) ------- AVERAGE (MAP_POPULATE) -------- VFIO MAP DMA in 0.268 s (59.6 GB/s) ------- AVERAGE (HUGETLBFS) -------- VFIO MAP DMA in 0.051 s (310.9 GB/s) With this patch: ------- AVERAGE (MADV_HUGEPAGE) -------- VFIO MAP DMA in 0.025 s (629.8 GB/s) ------- AVERAGE (MAP_POPULATE) -------- VFIO MAP DMA in 0.253 s (63.1 GB/s) ------- AVERAGE (HUGETLBFS) -------- VFIO MAP DMA in 0.030 s (530.5 GB/s) For large folio, we achieve an over 40% performance improvement. For small folios, the performance test results indicate a slight improvement. Signed-off-by: Li Zhe <lizhe.67@bytedance.com> Co-developed-by: Alex Williamson <alex.williamson@redhat.com> Acked-by: David Hildenbrand <david@redhat.com> Tested-by: Eric Farman <farman@linux.ibm.com> Link: https://lore.kernel.org/r/20250814064714.56485-3-lizhe.67@bytedance.com Signed-off-by: Alex Williamson <alex.williamson@redhat.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.