mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-11-01 00:48:50 +00:00
No description
7296f2301a
With CONFIG_SWIOTLB_DYNAMIC enabled, each round-trip map/unmap pair in the swiotlb results in 6 calls to swiotlb_find_pool(). In multiple places, the pool is found and used in one function, and then must be found again in the next function that is called because only the tlb_addr is passed as an argument. These are the six call sites: dma_direct_map_page: 1. swiotlb_map -> swiotlb_tbl_map_single -> swiotlb_bounce dma_direct_unmap_page: 2. dma_direct_sync_single_for_cpu -> is_swiotlb_buffer 3. dma_direct_sync_single_for_cpu -> swiotlb_sync_single_for_cpu -> swiotlb_bounce 4. is_swiotlb_buffer 5. swiotlb_tbl_unmap_single -> swiotlb_del_transient 6. swiotlb_tbl_unmap_single -> swiotlb_release_slots Reduce the number of calls by finding the pool at a higher level, and passing it as an argument instead of searching again. A key change is for is_swiotlb_buffer() to return a pool pointer instead of a boolean, and then pass this pool pointer to subsequent swiotlb functions. There are 9 occurrences of is_swiotlb_buffer() used to test if a buffer is a swiotlb buffer before calling a swiotlb function. To reduce code duplication in getting the pool pointer and passing it as an argument, introduce inline wrappers for this pattern. The generated code is essentially unchanged. Since is_swiotlb_buffer() no longer returns a boolean, rename some functions to reflect the change: * swiotlb_find_pool() becomes __swiotlb_find_pool() * is_swiotlb_buffer() becomes swiotlb_find_pool() * is_xen_swiotlb_buffer() becomes xen_swiotlb_find_pool() With these changes, a round-trip map/unmap pair requires only 2 pool lookups (listed using the new names and wrappers): dma_direct_unmap_page: 1. dma_direct_sync_single_for_cpu -> swiotlb_find_pool 2. swiotlb_tbl_unmap_single -> swiotlb_find_pool These changes come from noticing the inefficiencies in a code review, not from performance measurements. With CONFIG_SWIOTLB_DYNAMIC, __swiotlb_find_pool() is not trivial, and it uses an RCU read lock, so avoiding the redundant calls helps performance in a hot path. When CONFIG_SWIOTLB_DYNAMIC is *not* set, the code size reduction is minimal and the perf benefits are likely negligible, but no harm is done. No functional change is intended. Signed-off-by: Michael Kelley <mhklinux@outlook.com> Reviewed-by: Petr Tesarik <petr@tesarici.cz> Signed-off-by: Christoph Hellwig <hch@lst.de> |
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.