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b898b8c99e
io_sqd_handle_event() just does a mutex unlock/lock dance when it's supposed to park, somewhat relying on full ordering with the thread trying to park it which does a similar unlock/lock dance on sqd->lock. However, with adaptive spinning on mutexes, this can waste an awful lot of time. Normally this isn't very noticeable, as parking and unparking the thread isn't a common (or fast path) occurence. However, in testing ring resizing, it's testing exactly that, as each resize will require the SQPOLL to safely park and unpark. Have io_sq_thread_park() explicitly wait on sqd->park_pending being zero before attempting to grab the sqd->lock again. In a resize test, this brings the runtime of SQPOLL down from about 60 seconds to a few seconds, just like the !SQPOLL tests. And saves a ton of spinning time on the mutex, on both sides. 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 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.