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d34e798094
The function "can_migrate_task()" utilize "for_each_cpu_and" with a "if" statement inside to find the destination cpu. It's the same logic to find the first set bit of the result of the bitwise-AND of "env->dst_grpmask", "env->cpus" and "p->cpus_ptr". Refactor it by using "cpumask_first_and_and()" to perform bitwise-AND for "env->dst_grpmask", "env->cpus" and "p->cpus_ptr" and pick the first cpu within the intersection as the destination cpu, so we can elimate the need of looping and multiple times of branch. After the refactoring this part of the code can speed up from ~115ns to ~54ns, according to the test below. Ran the test for 5 times and the result is showned in the following table, and the test script is paste in next section. ------------------------------------------------------- |Old method| 130| 118| 115| 109| 106| avg ~115ns| ------------------------------------------------------- |New method| 58| 55| 54| 48| 55| avg ~54ns| ------------------------------------------------------- Signed-off-by: I Hsin Cheng <richard120310@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20250210103019.283824-1-richard120310@gmail.com |
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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.