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CPU scheduler marks need_resched flag to signal a schedule() on a particular CPU. But, schedule() may not happen immediately in cases where the current task is executing in the kernel mode (no preemption state) for extended periods of time. This patch adds a warn_on if need_resched is pending for more than the time specified in sysctl resched_latency_warn_ms. If it goes off, it is likely that there is a missing cond_resched() somewhere. Monitoring is done via the tick and the accuracy is hence limited to jiffy scale. This also means that we won't trigger the warning if the tick is disabled. This feature (LATENCY_WARN) is default disabled. Signed-off-by: Paul Turner <pjt@google.com> Signed-off-by: Josh Don <joshdon@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210416212936.390566-1-joshdon@google.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.