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

From: Kumar Kartikeya Dwivedi <memxor@gmail.com>
To: Puranjay Mohan <puranjay@kernel.org>
Cc: "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>,
	"Björn Töpel" <bjorn@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>,
	puranjay12@gmail.com
Subject: Re: [PATCH bpf-next v2 2/2] riscv, bpf: inline bpf_get_smp_processor_id()
Date: Tue, 30 Apr 2024 21:18:42 +0200	[thread overview]
Message-ID: <CAP01T74ASv5t8O1SPZgsWhgymK3303x9z3mFroHNgaHEZdjoxA@mail.gmail.com> (raw)
In-Reply-To: <20240430175834.33152-3-puranjay@kernel.org>

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

For non-riscv bits (& fwiw):

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

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