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Using tasklets for disk verification can reduce IO latency. When there are accelerated hash instructions it is often better to compute the hash immediately using a tasklet rather than deferring verification to a work-queue. This reduces time spent waiting to schedule work-queue jobs, but requires spending slightly more time in interrupt context. If the dm-bufio cache does not have the required hashes we fallback to the work-queue implementation. FEC is only possible using work-queue because code to support the FEC feature may sleep. The following shows a speed comparison of random reads on a dm-verity device. The dm-verity device uses a 1G ramdisk for data and a 1G ramdisk for hashes. One test was run using tasklets and one test was run using the existing work-queue solution. Both tests were run when the dm-bufio cache was hot. The tasklet implementation performs significantly better since there is no time spent waiting for work-queue jobs to be scheduled. READ: bw=181MiB/s (190MB/s), 181MiB/s-181MiB/s (190MB/s-190MB/s), io=512MiB (537MB), run=2827-2827msec READ: bw=23.6MiB/s (24.8MB/s), 23.6MiB/s-23.6MiB/s (24.8MB/s-24.8MB/s), io=512MiB (537MB), run=21688-21688msec 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.