linux-kernel - Re: [PATCH bpf-next v4 1/2] powerpc64/bpf: Support internal-only MOV instruction to resolve per-CPU addrs

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Message-ID: <ea212ba7-5118-409c-b082-efe3e360d73f@linux.ibm.com>
Date: Wed, 17 Dec 2025 10:41:17 +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 1/2] powerpc64/bpf: Support internal-only MOV
 instruction to resolve per-CPU addrs



On 10/12/25 12:20 pm, Saket Kumar Bhaskar wrote:
> With the introduction of commit 7bdbf7446305 ("bpf: add special
> internal-only MOV instruction to resolve per-CPU addrs"),
> a new BPF instruction BPF_MOV64_PERCPU_REG has been added to
> resolve absolute addresses of per-CPU data from their per-CPU
> offsets. This update requires enabling support for this
> instruction in the powerpc JIT compiler.
> 
> As of commit 7a0268fa1a36 ("[PATCH] powerpc/64: per cpu data
> optimisations"), the per-CPU data offset for the CPU is stored in
> the paca.
> 
> To support this BPF instruction in the powerpc JIT, the following
> powerpc instructions are emitted:
> if (IS_ENABLED(CONFIG_SMP))
> ld tmp1_reg, 48(13)		//Load per-CPU data offset from paca(r13) in tmp1_reg.
> add dst_reg, src_reg, tmp1_reg	//Add the per cpu offset to the dst.
> else if (src_reg != dst_reg)
> mr dst_reg, src_reg		//Move src_reg to dst_reg, if src_reg != dst_reg
> 
> To evaluate the performance improvements introduced by this change,
> the benchmark described in [1] was employed.
> 
> Before Change:
> glob-arr-inc   :   41.580 ± 0.034M/s
> arr-inc        :   39.592 ± 0.055M/s
> hash-inc       :   25.873 ± 0.012M/s
> 
> After Change:
> glob-arr-inc   :   42.024 ± 0.049M/s
> arr-inc        :   55.447 ± 0.031M/s
> hash-inc       :   26.565 ± 0.014M/s
> 
> [1] https://github.com/anakryiko/linux/commit/8dec900975ef
> 

Looks good to me.

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   |  5 +++++
>   arch/powerpc/net/bpf_jit_comp64.c | 10 ++++++++++
>   2 files changed, 15 insertions(+)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 5e976730b2f5..d53e9cd7563f 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -466,6 +466,11 @@ bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena)
>   	return true;
>   }
>   
> +bool bpf_jit_supports_percpu_insn(void)
> +{
> +	return IS_ENABLED(CONFIG_PPC64);
> +}
> +
>   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 1fe37128c876..37723ee9344e 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -918,6 +918,16 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
>   		case BPF_ALU | BPF_MOV | BPF_X: /* (u32) dst = src */
>   		case BPF_ALU64 | BPF_MOV | BPF_X: /* dst = src */
>   
> +			if (insn_is_mov_percpu_addr(&insn[i])) {
> +				if (IS_ENABLED(CONFIG_SMP)) {
> +					EMIT(PPC_RAW_LD(tmp1_reg, _R13, offsetof(struct paca_struct, data_offset)));
> +					EMIT(PPC_RAW_ADD(dst_reg, src_reg, tmp1_reg));
> +				} else if (src_reg != dst_reg) {
> +					EMIT(PPC_RAW_MR(dst_reg, src_reg));
> +				}
> +				break;
> +			}
> +
>   			if (insn_is_cast_user(&insn[i])) {
>   				EMIT(PPC_RAW_RLDICL_DOT(tmp1_reg, src_reg, 0, 32));
>   				PPC_LI64(dst_reg, (ctx->user_vm_start & 0xffffffff00000000UL));