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75fe4c0b3e
Inline calls to bpf_get_smp_processor_id() helper in the JIT by emitting
a read from struct thread_info. The SP_EL0 system register holds the
pointer to the task_struct and thread_info is the first member of this
struct. We can read the cpu number from the thread_info.
Here is how the ARM64 JITed assembly changes after this commit:
ARM64 JIT
===========
BEFORE AFTER
-------- -------
int cpu = bpf_get_smp_processor_id(); int cpu = bpf_get_smp_processor_id();
mov x10, #0xfffffffffffff4d0 mrs x10, sp_el0
movk x10, #0x802b, lsl #16 ldr w7, [x10, #24]
movk x10, #0x8000, lsl #32
blr x10
add x7, x0, #0x0
Performance improvement using benchmark[1]
./benchs/run_bench_trigger.sh glob-arr-inc arr-inc hash-inc
+---------------+-------------------+-------------------+--------------+
| Name | Before | After | % change |
|---------------+-------------------+-------------------+--------------|
| glob-arr-inc | 23.380 ± 1.675M/s | 25.893 ± 0.026M/s | + 10.74% |
| arr-inc | 23.928 ± 0.034M/s | 25.213 ± 0.063M/s | + 5.37% |
| hash-inc | 12.352 ± 0.005M/s | 12.609 ± 0.013M/s | + 2.08% |
+---------------+-------------------+-------------------+--------------+
[1]
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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.