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The runtime cost of joining a single multicast group in the current implementation of ____ip_mc_inc_group grows linearly with the number of existing memberships. This is caused by the linear search for an existing group record in the multicast address list. This linear complexity results in quadratic complexity when successively adding memberships, which becomes a performance bottleneck when setting up large numbers of multicast memberships. If available, use the existing multicast hash map mc_hash to quickly search for an existing group membership record. This leads to near-constant complexity on the addition of a new multicast record, significantly improving performance for workloads involving many multicast memberships. On profiling with a loopback device, this patch presented a speedup of around 6 when successively setting up 2000 multicast groups using setsockopt without measurable drawbacks on smaller numbers of multicast groups. Signed-off-by: Jonas Rebmann <jre@pengutronix.de> Reviewed-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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.