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Profiling shows that calling nr_possible_cpus() in objpool_pop() takes a noticeable amount of CPU (when profiled on 80-core machine), as we need to recalculate number of set bits in a CPU bit mask. This number can't change, so there is no point in paying the price for recalculating it. As such, cache this value in struct objpool_head and use it in objpool_pop(). On the other hand, cached pool->nr_cpus isn't necessary, as it's not used in hot path and is also a pretty trivial value to retrieve. So drop pool->nr_cpus in favor of using nr_cpu_ids everywhere. This way the size of struct objpool_head remains the same, which is a nice bonus. Same BPF selftests benchmarks were used to evaluate the effect. Using changes in previous patch (inlining of objpool_pop/objpool_push) as baseline, here are the differences: BASELINE ======== kretprobe : 9.937 ± 0.174M/s kretprobe-multi: 10.440 ± 0.108M/s AFTER ===== kretprobe : 10.106 ± 0.120M/s (+1.7%) kretprobe-multi: 10.515 ± 0.180M/s (+0.7%) Link: https://lore.kernel.org/all/20240424215214.3956041-3-andrii@kernel.org/ Cc: Matt (Qiang) Wu <wuqiang.matt@bytedance.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
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.