19c56d4e5b
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. RISC-V uses generic per-cpu implementation where the offsets for CPUs are kept in an array called __per_cpu_offset[cpu_number]. RISCV stores the address of the task_struct in TP register. The first element in task_struct is struct thread_info, and we can get the cpu number by reading from the TP register + offsetof(struct thread_info, cpu). Once we have the cpu number in a register we read the offset for that cpu from address: &__per_cpu_offset + cpu_number << 3. Then we add this offset to the destination register. To measure the improvement from this change, the benchmark in [1] was used on Qemu: Before: glob-arr-inc : 1.127 ± 0.013M/s arr-inc : 1.121 ± 0.004M/s hash-inc : 0.681 ± 0.052M/s After: glob-arr-inc : 1.138 ± 0.011M/s arr-inc : 1.366 ± 0.006M/s hash-inc : 0.676 ± 0.001M/s [1] https://github.com/anakryiko/linux/commit/8dec900975ef Signed-off-by: Puranjay Mohan <puranjay@kernel.org> Acked-by: Björn Töpel <bjorn@kernel.org> Link: https://lore.kernel.org/r/20240502151854.9810-2-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.