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While doing newidle load balancing, it is possible for new tasks to arrive, such as with pending wakeups. newidle_balance() already accounts for this by exiting the sched_domain load_balance() iteration if it detects these cases. This is very important for minimizing wakeup latency. However, if we are already in load_balance(), we may stay there for a while before returning back to newidle_balance(). This is most exacerbated if we enter a 'goto redo' loop in the LBF_ALL_PINNED case. A very straightforward workaround to this is to adjust should_we_balance() to bail out if we're doing a CPU_NEWLY_IDLE balance and new tasks are detected. This was tested with the following reproduction: - two threads that take turns sleeping and waking each other up are affined to two cores - a large number of threads with 100% utilization are pinned to all other cores Without this patch, wakeup latency was ~120us for the pair of threads, almost entirely spent in load_balance(). With this patch, wakeup latency is ~6us. Signed-off-by: Josh Don <joshdon@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20220609025515.2086253-1-joshdon@google.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 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.