linux-kernel - Re: [PATCH bpf-next v2 2/2] riscv, bpf: inline bpf_get_smp_processor

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Date: Thu, 02 May 2024 18:19:04 +0200
From: Björn Töpel <bjorn@...nel.org>
To: Puranjay Mohan <puranjay@...nel.org>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Eduard
 Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, Yonghong Song
 <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, KP
 Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou
 <aou@...s.berkeley.edu>, bpf@...r.kernel.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, Pu Lehui
 <pulehui@...wei.com>
Cc: puranjay12@...il.com
Subject: Re: [PATCH bpf-next v2 2/2] riscv, bpf: inline
 bpf_get_smp_processor_id()

Puranjay Mohan <puranjay@...nel.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@...nel.org>

Acked-by: Björn Töpel <bjorn@...nel.org>