Re: [PATCH bpf-next v6 2/4] riscv, bpf: inline bpf_get_smp_processor_id()

From: Andrii Nakryiko
Date: Tue May 07 2024 - 17:11:58 EST


On Thu, May 2, 2024 at 8:19 AM Puranjay Mohan <puranjay@xxxxxxxxxx> 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@xxxxxxxxxx>
> Acked-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---

same about carrying over acks:

Acked-by: Björn Töpel <bjorn@xxxxxxxxxx>

> arch/riscv/net/bpf_jit_comp64.c | 26 ++++++++++++++++++++++++++
> include/linux/filter.h | 1 +
> kernel/bpf/core.c | 11 +++++++++++
> kernel/bpf/verifier.c | 4 ++++
> 4 files changed, 42 insertions(+)
>

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