7e55c60acf
raid5_make_request() loops through every page in the request, finds the appropriate stripe and adds the bio for that page in the disk. This causes a great deal of contention on the hash_lock and extra work seeing each stripe must be found once for every data disk. The number of times a stripe must be found can be reduced by pivoting raid5_make_request() so that it loops through every stripe and then loops through every disk in that stripe to see if the bio must be added. This reduces the number of times the hash lock must be taken by a factor equal to the number of data disks. To accomplish this, the logical sectors that have already been added must be tracked. Tracking them is done with a bitmap: the bits for all pages are set at the start of the request and each bit is cleared once the bio is added to a stripe. Finding the next sector to be done is then just a call to find_first_bit() so that sectors that have been done can simply be skipped. One minor downside is that the maximum sectors for a request must be limited so that the bitmap can be appropriately sized on the stack. This limit is arbitrarily chosen to be 256 stripe pages which works out to 1MB if PAGE_SIZE == DEFAULT_STRIPE_SIZE. This doesn't actually restrict the maximum request further seeing the default block queue settings are used which restricts the number of segments to 128 (which results in request sizes that are approximately 512KB). Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Signed-off-by: Song Liu <song@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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 Restructured Text 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.