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The function opencodes for_each_cpu() by using a plain for-loop. The loop calls cpumask_weight() inside the conditional section. Because cpumask_weight() is O(1), the overall complexity of the function is O(node * node_cpus^2). Also, cpumask_nth() internally calls hweight(), which, if not hardware accelerated, is slower than cpumask_next() in for_each_cpu(). If switched to the dedicated for_each_cpu(), the rebalance_wq_table() can drop calling cpumask_weight(), together with some housekeeping code. This makes the overall complexity O(node * node_cpus), or simply speaking O(nr_cpu_ids). While there, fix opencoded for_each_possible_cpu() too. Signed-off-by: Yury Norov <yury.norov@gmail.com> 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.