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From: =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>
To: Puranjay Mohan <puranjay@kernel.org>, Alexei Starovoitov
 <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, Andrii Nakryiko
 <andrii@kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>, Eduard
 Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>, Yonghong Song
 <yonghong.song@linux.dev>, John Fastabend <john.fastabend@gmail.com>, KP
 Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>, Hao Luo
 <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>, Paul Walmsley
 <paul.walmsley@sifive.com>, Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou
 <aou@eecs.berkeley.edu>, bpf@vger.kernel.org,
 linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Pu Lehui
 <pulehui@huawei.com>
Cc: puranjay12@gmail.com
Subject: Re: [PATCH bpf-next v2 2/2] riscv, bpf: inline
 bpf_get_smp_processor_id()
In-Reply-To: <20240430175834.33152-3-puranjay@kernel.org>
References: <20240430175834.33152-1-puranjay@kernel.org>
 <20240430175834.33152-3-puranjay@kernel.org>
Date: Thu, 02 May 2024 18:19:04 +0200
Message-ID: <87edakw5jb.fsf@all.your.base.are.belong.to.us>
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Puranjay Mohan <puranjay@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`
> 	  =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D
>
>                 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 =C2=B1 0.006M/s | 1.336 =C2=B1 0.010M/s |   + 24.=
04%   |
> | arr-inc       | 1.078 =C2=B1 0.002M/s | 1.332 =C2=B1 0.015M/s |   + 23.=
56%   |
> | hash-inc      | 0.494 =C2=B1 0.004M/s | 0.653 =C2=B1 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@kernel.org>

Acked-by: Bj=C3=B6rn T=C3=B6pel <bjorn@kernel.org>