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On mobile device high-load situations, permission check can happen more than 90,000/s (8 core system). With default 512 cache nodes configuration, avc cache miss happens more often and occasionally leads to long time (>2ms) irqs off on both big and little cores, which decreases system real-time capability. An actual call stack is as follows: => avc_compute_av => avc_perm_nonode => avc_has_perm_noaudit => selinux_capable => security_capable => capable => __sched_setscheduler => do_sched_setscheduler => __arm64_sys_sched_setscheduler => invoke_syscall => el0_svc_common => do_el0_svc => el0_svc => el0t_64_sync_handler => el0t_64_sync Although we can expand avc nodes through /sys/fs/selinux/cache_threshold to mitigate long time irqs off, hash conflicts make the bucket average length longer because of the fixed size of cache slots, leading to avc_search_node() latency increase. So introduce a new config to make avc cache slot size also configurable, and with fine tuning, we can mitigate long time irqs off with slightly avc_search_node() performance regression. Theoretically, the main overhead is memory consumption. Signed-off-by: Hongru Zhang <zhanghongru@xiaomi.com> Signed-off-by: Paul Moore <paul@paul-moore.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.