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7a4c32222b
Support an instruction for resolving absolute addresses of per-CPU
data from their per-CPU offsets. This instruction is internal-only and
users are not allowed to use them directly. They will only be used for
internal inlining optimizations for now between BPF verifier and BPF
JITs.
Since commit 7158627686 ("arm64: percpu: implement optimised pcpu
access using tpidr_el1"), the per-cpu offset for the CPU is stored in
the tpidr_el1/2 register of that CPU.
To support this BPF instruction in the ARM64 JIT, the following ARM64
instructions are emitted:
mov dst, src // Move src to dst, if src != dst
mrs tmp, tpidr_el1/2 // Move per-cpu offset of the current cpu in tmp.
add dst, dst, tmp // Add the per cpu offset to the dst.
To measure the performance improvement provided by this change, the
benchmark in [1] was used:
Before:
glob-arr-inc : 23.597 ± 0.012M/s
arr-inc : 23.173 ± 0.019M/s
hash-inc : 12.186 ± 0.028M/s
After:
glob-arr-inc : 23.819 ± 0.034M/s
arr-inc : 23.285 ± 0.017M/s
hash-inc : 12.419 ± 0.011M/s
[1] https://github.com/anakryiko/linux/commit/8dec900975ef
Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240502151854.9810-4-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@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.