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Commitc055e3eae0("crypto: xor - use ktime for template benchmarking") switched from using jiffies to ktime-based performance benchmarking. This works nicely on machines which have a fine-grained ktime() clocksource as e.g. x86 machines with TSC. But other machines, e.g. my 4-way HP PARISC server, don't have such fine-grained clocksources, which is why it seems that 800 xor loops take zero seconds, which then shows up in the logs as: xor: measuring software checksum speed 8regs : -1018167296 MB/sec 8regs_prefetch : -1018167296 MB/sec 32regs : -1018167296 MB/sec 32regs_prefetch : -1018167296 MB/sec Fix this with some small modifications to the existing code to improve the algorithm to always produce correct results without introducing major delays for architectures with a fine-grained ktime() clocksource: a) Delay start of the timing until ktime() just advanced. On machines with a fast ktime() this should be just one additional ktime() call. b) Count the number of loops. Run at minimum 800 loops and finish earliest when the ktime() counter has progressed. With that the throughput can now be calculated more accurately under all conditions. Fixes:c055e3eae0("crypto: xor - use ktime for template benchmarking") Signed-off-by: Helge Deller <deller@gmx.de> Tested-by: John David Anglin <dave.anglin@bell.net> v2: - clean up coding style (noticed & suggested by Herbert Xu) - rephrased & fixed typo in commit message Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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.