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Most modern hardware supports very fast accelerated crc32c calculation. If that is supported the CPU overhead of the checksum calculation is very limited, and offloading the calculation to special worker threads has a lot of overhead for no gain. E.g. on an Intel Optane device is actually very much slows down even 1M buffered writes with fio: Unpatched: write: IOPS=3316, BW=3316MiB/s (3477MB/s)(200GiB/61757msec); 0 zone resets With synchronous CRCs: write: IOPS=4882, BW=4882MiB/s (5119MB/s)(200GiB/41948msec); 0 zone resets With a lot of variation during the unpatched run going down as low as 1100MB/s, while the synchronous CRC version has about the same peak write speed but much lower dips, and fewer kworkers churning around. Both tests had fio saturated at 100% CPU. (thanks to Jens Axboe via Chris Mason for the benchmarking) Reviewed-by: Chris Mason <clm@fb.com> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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.