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Ryan Newton
44f5c8ec5b
The builtin DSQ queue data structures are meant to be used by a wide range of different sched_ext schedulers with different demands on these data structures. They might be per-cpu with low-contention, or high-contention shared queues. Unfortunately, DSQs have a coarse-grained lock around the whole data structure. Without going all the way to a lock-free, more scalable implementation, a small step we can take to reduce lock contention is to allow a lockless, small-fixed-cost peek at the head of the queue. This change allows certain custom SCX schedulers to cheaply peek at queues, e.g. during load balancing, before locking them. But it represents a few extra memory operations to update the pointer each time the DSQ is modified, including a memory barrier on ARM so the write appears correctly ordered. This commit adds a first_task pointer field which is updated atomically when the DSQ is modified, and allows any thread to peek at the head of the queue without holding the lock. Signed-off-by: Ryan Newton <newton@meta.com> Reviewed-by: Andrea Righi <arighi@nvidia.com> Reviewed-by: Christian Loehle <christian.loehle@arm.com> Signed-off-by: Tejun Heo <tj@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 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.