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In the bypass mode, the global DSQ is used to schedule all tasks in simple FIFO order. All tasks are queued into the global DSQ and all CPUs try to execute tasks from it. This creates a lot of cross-node cacheline accesses and scheduling across the node boundaries, and can lead to live-lock conditions where the system takes tens of minutes to disable the BPF scheduler while executing in the bypass mode. Split the global DSQ per NUMA node. Each node has its own global DSQ. When a task is dispatched to SCX_DSQ_GLOBAL, it's put into the global DSQ local to the task's CPU and all CPUs in a node only consume its node-local global DSQ. This resolves a livelock condition which could be reliably triggered on an 2x EPYC 7642 system by running `stress-ng --race-sched 1024` together with `stress-ng --workload 80 --workload-threads 10` while repeatedly enabling and disabling a SCX scheduler. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: David Vernet <void@manifault.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 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.