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441b8a7803
Replace drain checks with one-way flag set upon seeing the first IOSQE_IO_DRAIN request. There are several places where it cuts cycles well: 1) It's much faster than the fast check with two conditions in io_drain_req() including pretty complex list_empty_careful(). 2) We can mark io_queue_sqe() inline now, that's a huge win. 3) It replaces timeout and drain checks in io_commit_cqring() with a single flags test. Also great not touching ->defer_list there without a reason so limiting cache bouncing. It adds a small amount of overhead to drain path, but it's negligible. The main nuisance is that once it meets any DRAIN request in io_uring instance lifetime it will _always_ go through a slower path, so drain-less and offset-mode timeout less applications are preferable. The overhead in that case would be not big, but it's worth to bear in mind. Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> Link: https://lore.kernel.org/r/98d2fff8c4da5144bb0d08499f591d4768128ea3.1623709150.git.asml.silence@gmail.com 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.