linux-kernel - Re: [PATCH 2/2] powerpc, bpf: Inline bpf_get_smp_processor

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Message-ID: <61e746ca-456f-4824-9678-85399b450bce@csgroup.eu>
Date: Tue, 11 Mar 2025 18:51:28 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Saket Kumar Bhaskar <skb99@...ux.ibm.com>, bpf@...r.kernel.org,
 linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc: ast@...nel.org, hbathini@...ux.ibm.com, andrii@...nel.org,
 daniel@...earbox.net, martin.lau@...ux.dev, eddyz87@...il.com,
 song@...nel.org, yonghong.song@...ux.dev, john.fastabend@...il.com,
 kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
 naveen@...nel.org, maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com
Subject: Re: [PATCH 2/2] powerpc, bpf: Inline bpf_get_smp_processor_id()



Le 11/03/2025 à 17:09, Saket Kumar Bhaskar a écrit :
> [Vous ne recevez pas souvent de courriers de skb99@...ux.ibm.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> Inline the calls to bpf_get_smp_processor_id() in the powerpc bpf jit.
> 
> powerpc saves the Logical processor number (paca_index) 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  | 41.580 ± 0.034M/s | 54.137 ± 0.019M/s |   + 30.20%   |
> | arr-inc       | 39.592 ± 0.055M/s | 54.000 ± 0.026M/s |   + 36.39%   |
> | hash-inc      | 25.873 ± 0.012M/s | 26.334 ± 0.058M/s |   + 1.78%    |
> +---------------+-------------------+-------------------+--------------+
> 

Nice improvement.

I see that bpf_get_current_task() could be inlined as well, on PPC32 it 
is in r2, on PPC64 it is in paca.

> [1] https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fanakryiko%2Flinux%2Fcommit%2F8dec900975ef&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C1d1f40ce41344cf1ecf508dd60b73ae0%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638773062267813839%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=T%2BG206FHtW7hhFT1%2BXxRwN7pc%2BRzu8SiMlZ5njIlhB8%3D&reserved=0
> 
> Signed-off-by: Saket Kumar Bhaskar <skb99@...ux.ibm.com>
> ---
>   arch/powerpc/net/bpf_jit_comp.c   | 10 ++++++++++
>   arch/powerpc/net/bpf_jit_comp64.c |  5 +++++
>   2 files changed, 15 insertions(+)
> 
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 3d4bd45a9a22..4b79b2d95469 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -445,6 +445,16 @@ bool bpf_jit_supports_percpu_insn(void)
>          return true;
>   }
> 
> +bool bpf_jit_inlines_helper_call(s32 imm)
> +{
> +       switch (imm) {
> +       case BPF_FUNC_get_smp_processor_id:
> +               return true;
> +       default:
> +               return false;
> +       }
> +}

What about PPC32 ?


> +
>   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 06f06770ceea..a8de12c026da 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -1087,6 +1087,11 @@ 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 (insn[i].src_reg == 0 && imm == BPF_FUNC_get_smp_processor_id) {

Please use BPF_REG_0 instead of just 0.

> +                               EMIT(PPC_RAW_LHZ(bpf_to_ppc(BPF_REG_0), _R13, offsetof(struct paca_struct, paca_index)));

Can just use 'src_reg' instead of 'bpf_to_ppc(BPF_REG_0)'

> +                               break;
> +                       }
> +
>                          ret = bpf_jit_get_func_addr(fp, &insn[i], extra_pass,
>                                                      &func_addr, &func_addr_fixed);
>                          if (ret < 0)
> --
> 2.43.5
>