[bpf-next,v2,0/2] riscv, bpf: Support per-CPU insn and inline bpf_get_smp_processor_id()

Message

Puranjay Mohan April 30, 2024, 5:58 p.m. UTC

Changes in v1->v2:
v1: https://lore.kernel.org/all/[e-mail]/
- Use emit_addr() in place of emit_imm() in the first patch.
- Add the second patch to inline bpf_get_smp_processor_id()

The first patch add the support for the internal-only MOV instruction to
resolve per-CPU addrs to absolute addresses.
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).

The second patch inlines the calls bpf_get_smp_processor_id() in the JIT
by emitting a load from the TP + offsetof(struct thread_info, cpu).

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%   |
  +---------------+------------------+------------------+--------------+

[1] https://github.com/anakryiko/linux/commit/8dec900975ef

Puranjay Mohan (2):
  riscv, bpf: add internal-only MOV instruction to resolve per-CPU addrs
  riscv, bpf: inline bpf_get_smp_processor_id()

 arch/riscv/net/bpf_jit_comp64.c | 50 +++++++++++++++++++++++++++++++++
 include/linux/filter.h          |  1 +
 kernel/bpf/core.c               | 11 ++++++++
 kernel/bpf/verifier.c           |  2 ++
 4 files changed, 64 insertions(+)