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WQ_HIGHPRI increases throughput and decreases disk latency when using dm-verity. This is important in Android for camera startup speed. The following tests were run by doing 60 seconds of random reads using a dm-verity device backed by two ramdisks. Without WQ_HIGHPRI lat (usec): min=13, max=3947, avg=69.53, stdev=50.55 READ: bw=51.1MiB/s (53.6MB/s), 51.1MiB/s-51.1MiB/s (53.6MB/s-53.6MB/s) With WQ_HIGHPRI: lat (usec): min=13, max=7854, avg=31.15, stdev=30.42 READ: bw=116MiB/s (121MB/s), 116MiB/s-116MiB/s (121MB/s-121MB/s) Further testing was done by measuring how long it takes to open a camera on an Android device. Without WQ_HIGHPRI Total verity work queue wait times (ms): 880.960, 789.517, 898.852 With WQ_HIGHPRI: Total verity work queue wait times (ms): 528.824, 439.191, 433.300 The average time to open the camera is reduced by 350ms (or 40-50%). Signed-off-by: Nathan Huckleberry <nhuck@google.com> Signed-off-by: Mike Snitzer <snitzer@kernel.org>
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.