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If one is monitoring 6 events on 20 cgroups the per-CPU RB tree will hold 120 events. The scheduling in of the events currently iterates over all events looking to see which events match the task's cgroup or its cgroup hierarchy. If a task is in 1 cgroup with 6 events, then 114 events are considered unnecessarily. This change orders events in the RB tree by cgroup id if it is present. This means scheduling in may go directly to events associated with the task's cgroup if one is present. The per-CPU iterator storage in visit_groups_merge is sized sufficent for an iterator per cgroup depth, where different iterators are needed for the task's cgroup and parent cgroups. By considering the set of iterators when visiting, the lowest group_index event may be selected and the insertion order group_index property is maintained. This also allows event rotation to function correctly, as although events are grouped into a cgroup, rotation always selects the lowest group_index event to rotate (delete/insert into the tree) and the min heap of iterators make it so that the group_index order is maintained. Signed-off-by: Ian Rogers <irogers@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20190724223746.153620-3-irogers@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.