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Using per-cpu storage for @x86_cpu_to_logical_apicid is not optimal. Broadcast IPI will need at least one cache line per cpu to access this field. __x2apic_send_IPI_mask() is using standard bitmask operators. By converting x86_cpu_to_logical_apicid to an array, we divide by 16x number of needed cache lines, because we find 16 values per cache line. CPU prefetcher can kick nicely. Also move @cluster_masks to READ_MOSTLY section to avoid false sharing. Tested on a dual socket host with 256 cpus, cost for a full broadcast is now 11 usec instead of 33 usec. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20211007143556.574911-1-eric.dumazet@gmail.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.