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Add a test for comparing the performance of RCU with various read-side synchronization mechanisms. The test has proved useful for collecting data and performing these comparisons. Currently RCU, SRCU, reader-writer lock, reader-writer semaphore and reference counting can be measured using refperf.perf_type parameter. Each invocation of the test runs measures performance of a specific mechanism. The maximum number of CPUs to concurrently run readers on is chosen by the test itself and is 75% of the total number of CPUs. So if you had 24 CPUs, the test runs with a maximum of 18 parallel readers. A number of experiments are conducted, and in each experiment, the number of readers is increased by 1, upto the 75% of CPUs mark. During each experiment, all readers execute an empty loop with refperf.loops iterations and time the total loop duration. This is then averaged. Example output: Parameters "refperf.perf_type=srcu refperf.loops=2000000" looks like: [ 3.347133] srcu-ref-perf: [ 3.347133] Threads Time(ns) [ 3.347133] 1 36 [ 3.347133] 2 34 [ 3.347133] 3 34 [ 3.347133] 4 34 [ 3.347133] 5 33 [ 3.347133] 6 33 [ 3.347133] 7 33 [ 3.347133] 8 33 [ 3.347133] 9 33 [ 3.347133] 10 33 [ 3.347133] 11 33 [ 3.347133] 12 33 [ 3.347133] 13 33 [ 3.347133] 14 33 [ 3.347133] 15 32 [ 3.347133] 16 33 [ 3.347133] 17 33 [ 3.347133] 18 34 Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@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.