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d4755e1538
io_uring hashes writes to a given file/inode so that it can serialize them. This is useful if the file system needs exclusive access to the file to perform the write, as otherwise we end up with a ton of io-wq threads trying to lock the inode at the same time. This can cause excessive system time. But if the file system has flagged that it supports parallel O_DIRECT writes, then there's no need to serialize the writes. Check for that through FMODE_DIO_PARALLEL_WRITE and don't hash it if we don't need to. In a basic test of 8 threads writing to a file on XFS on a gen2 Optane, with each thread writing in 4k chunks, it improves performance from ~1350K IOPS (or ~5290MiB/sec) to ~1410K IOPS (or ~5500MiB/sec). Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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.