linux-kernel - Re: [PATCH bpf-next v4 2/2] powerpc64/bpf: Inline bpf_get_smp_processor_id() and bpf_get_current_task/

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Message-ID: <a8345e11-d0b4-4000-9f2c-b02f01c8df44@linux.ibm.com>
Date: Wed, 17 Dec 2025 10:42:10 +0530
From: Hari Bathini <hbathini@...ux.ibm.com>
To: Saket Kumar Bhaskar <skb99@...ux.ibm.com>, bpf@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc: sachinpb@...ux.ibm.com, venkat88@...ux.ibm.com, andrii@...nel.org,
        eddyz87@...il.com, ast@...nel.org, daniel@...earbox.net,
        martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
        haoluo@...gle.com, jolsa@...nel.org, christophe.leroy@...roup.eu,
        naveen@...nel.org, maddy@...ux.ibm.com, mpe@...erman.id.au,
        npiggin@...il.com
Subject: Re: [PATCH bpf-next v4 2/2] powerpc64/bpf: Inline
 bpf_get_smp_processor_id() and bpf_get_current_task/_btf()



On 10/12/25 12:20 pm, Saket Kumar Bhaskar wrote:
> Inline the calls to bpf_get_smp_processor_id() and bpf_get_current_task/_btf()
> in the powerpc bpf jit.
> 
> powerpc saves the Logical processor number (paca_index) and pointer
> to current task (__current) in paca.
> 
> Here is how the powerpc JITed assembly changes after this commit:
> 
> Before:
> 
> cpu = bpf_get_smp_processor_id();
> 
> addis 12, 2, -517
> addi 12, 12, -29456
> mtctr 12
> bctrl
> mr	8, 3
> 
> After:
> 
> cpu = bpf_get_smp_processor_id();
> 
> lhz 8, 8(13)
> 
> To evaluate the performance improvements introduced by this change,
> the benchmark described in [1] was employed.
> 
> +---------------+-------------------+-------------------+--------------+
> |      Name     |      Before       |        After      |   % change   |
> |---------------+-------------------+-------------------+--------------|
> | glob-arr-inc  | 40.701 ± 0.008M/s | 55.207 ± 0.021M/s |   + 35.64%   |
> | arr-inc       | 39.401 ± 0.007M/s | 56.275 ± 0.023M/s |   + 42.42%   |
> | hash-inc      | 24.944 ± 0.004M/s | 26.212 ± 0.003M/s |   +  5.08%   |
> +---------------+-------------------+-------------------+--------------+
> 
> [1] https://github.com/anakryiko/linux/commit/8dec900975ef
> 

Looks good.

Acked-by: Hari Bathini <hbathini@...ux.ibm.com>


> Reviewed-by: Puranjay Mohan <puranjay@...nel.org>
> Signed-off-by: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
> ---
>   arch/powerpc/net/bpf_jit_comp.c   | 12 ++++++++++++
>   arch/powerpc/net/bpf_jit_comp64.c | 11 +++++++++++
>   2 files changed, 23 insertions(+)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index d53e9cd7563f..b243ee205885 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -471,6 +471,18 @@ bool bpf_jit_supports_percpu_insn(void)
>   	return IS_ENABLED(CONFIG_PPC64);
>   }
>   
> +bool bpf_jit_inlines_helper_call(s32 imm)
> +{
> +	switch (imm) {
> +	case BPF_FUNC_get_smp_processor_id:
> +	case BPF_FUNC_get_current_task:
> +	case BPF_FUNC_get_current_task_btf:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
>   void *arch_alloc_bpf_trampoline(unsigned int size)
>   {
>   	return bpf_prog_pack_alloc(size, bpf_jit_fill_ill_insns);
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 37723ee9344e..6c827e7aa691 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -1400,6 +1400,17 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
>   		case BPF_JMP | BPF_CALL:
>   			ctx->seen |= SEEN_FUNC;
>   
> +			if (src_reg == bpf_to_ppc(BPF_REG_0)) {
> +				if (imm == BPF_FUNC_get_smp_processor_id) {
> +					EMIT(PPC_RAW_LHZ(src_reg, _R13, offsetof(struct paca_struct, paca_index)));
> +					break;
> +				} else if (imm == BPF_FUNC_get_current_task ||
> +					   imm == BPF_FUNC_get_current_task_btf) {
> +					EMIT(PPC_RAW_LD(src_reg, _R13, offsetof(struct paca_struct, __current)));
> +					break;
> +				}
> +			}
> +
>   			ret = bpf_jit_get_func_addr(fp, &insn[i], extra_pass,
>   						    &func_addr, &func_addr_fixed);
>   			if (ret < 0)