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

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Date: Tue, 30 Apr 2024 21:18:42 +0200
From: Kumar Kartikeya Dwivedi <memxor@...il.com>
To: Puranjay Mohan <puranjay@...nel.org>
Cc: 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>, Björn Töpel <bjorn@...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>, puranjay12@...il.com
Subject: Re: [PATCH bpf-next v2 2/2] riscv, bpf: inline bpf_get_smp_processor_id()

On Tue, 30 Apr 2024 at 20:00, Puranjay Mohan <puranjay@...nel.org> wrote:
>
> 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>
> ---

For non-riscv bits (& fwiw):

Acked-by: Kumar Kartikeya Dwivedi <memxor@...il.com>