[PATCH bpf-next v2 2/2] riscv, bpf: inline bpf_get_smp_processor_id()

[Björn Töpel]

Puranjay Mohan <puranjay at kernel.org> writes:

> Inline the calls to bpf_get_smp_processor_id() in the riscv bpf jit.
>
> RISCV saves the pointer to the CPU's task_struct in the TP (thread
> pointer) register. This makes it trivial to get the CPU's processor id.
> As thread_info is the first member of task_struct, we can read the
> processor id from TP + offsetof(struct thread_info, cpu).
>
>           RISCV64 JIT output for `call bpf_get_smp_processor_id`
> 	  ======================================================
>
>                 Before                           After
>                --------                         -------
>
>          auipc   t1,0x848c                  ld    a5,32(tp)
>          jalr    604(t1)
>          mv      a5,a0
>
> Benchmark using [1] on Qemu.
>
> ./benchs/run_bench_trigger.sh glob-arr-inc arr-inc hash-inc
>
> +---------------+------------------+------------------+--------------+
> |      Name     |     Before       |       After      |   % change   |
> |---------------+------------------+------------------+--------------|
> | glob-arr-inc  | 1.077 ± 0.006M/s | 1.336 ± 0.010M/s |   + 24.04%   |
> | arr-inc       | 1.078 ± 0.002M/s | 1.332 ± 0.015M/s |   + 23.56%   |
> | hash-inc      | 0.494 ± 0.004M/s | 0.653 ± 0.001M/s |   + 32.18%   |
> +---------------+------------------+------------------+--------------+
>
> NOTE: This benchmark includes changes from this patch and the previous
>       patch that implemented the per-cpu insn.
>
> [1] https://github.com/anakryiko/linux/commit/8dec900975ef
>
> Signed-off-by: Puranjay Mohan <puranjay at kernel.org>

Acked-by: Björn Töpel <bjorn at kernel.org>