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Message-ID: <CAEf4BzZOFye13KdBUKA7E=41NVNy5fOzF3bxFzaeZAzkq0kh-w@mail.gmail.com>
Date: Wed, 24 Apr 2024 15:01:43 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Puranjay Mohan <puranjay@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>,
Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Zi Shen Lim <zlim.lnx@...il.com>, Xu Kuohai <xukuohai@...wei.com>,
Florent Revest <revest@...omium.org>, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, bpf@...r.kernel.org, puranjay12@...il.com
Subject: Re: [PATCH bpf-next v2 2/2] bpf, arm64: inline bpf_get_smp_processor_id()
helper
On Wed, Apr 24, 2024 at 10:36 AM Puranjay Mohan <puranjay@...nel.org> wrote:
>
> As ARM64 JIT now implements BPF_MOV64_PERCPU_REG instruction, inline
> bpf_get_smp_processor_id().
>
> ARM64 uses the per-cpu variable cpu_number to store the cpu id.
>
> Here is how the BPF and ARM64 JITed assembly changes after this commit:
>
> BPF
> =====
> BEFORE AFTER
> -------- -------
>
> int cpu = bpf_get_smp_processor_id(); int cpu = bpf_get_smp_processor_id();
> (85) call bpf_get_smp_processor_id#229032 (18) r0 = 0xffff800082072008
> (bf) r0 = r0
nit: hmm, you are probably using a bit outdated bpftool, it should be
emitted as:
(bf) r0 = &(void __percpu *)(r0)
> (61) r0 = *(u32 *)(r0 +0)
>
> ARM64 JIT
> ===========
>
> BEFORE AFTER
> -------- -------
>
> int cpu = bpf_get_smp_processor_id(); int cpu = bpf_get_smp_processor_id();
> mov x10, #0xfffffffffffff4d0 mov x7, #0xffff8000ffffffff
> movk x10, #0x802b, lsl #16 movk x7, #0x8207, lsl #16
> movk x10, #0x8000, lsl #32 movk x7, #0x2008
> blr x10 mrs x10, tpidr_el1
> add x7, x0, #0x0 add x7, x7, x10
> ldr w7, [x7]
>
> Performance improvement using benchmark[1]
>
> BEFORE AFTER
> -------- -------
>
> glob-arr-inc : 23.817 ± 0.019M/s glob-arr-inc : 24.631 ± 0.027M/s
> arr-inc : 23.253 ± 0.019M/s arr-inc : 23.742 ± 0.023M/s
> hash-inc : 12.258 ± 0.010M/s hash-inc : 12.625 ± 0.004M/s
>
> [1] https://github.com/anakryiko/linux/commit/8dec900975ef
>
> Signed-off-by: Puranjay Mohan <puranjay@...nel.org>
> ---
> kernel/bpf/verifier.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
Besides the nits, lgtm.
Acked-by: Andrii Nakryiko <andrii@...nel.org>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 9715c88cc025..3373be261889 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -20205,7 +20205,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> goto next_insn;
> }
>
> -#ifdef CONFIG_X86_64
> +#if defined(CONFIG_X86_64) || defined(CONFIG_ARM64)
I think you can drop this, we are protected by
bpf_jit_supports_percpu_insn() check and newly added inner #if/#elif
checks?
> /* Implement bpf_get_smp_processor_id() inline. */
> if (insn->imm == BPF_FUNC_get_smp_processor_id &&
> prog->jit_requested && bpf_jit_supports_percpu_insn()) {
> @@ -20214,11 +20214,20 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> * changed in some incompatible and hard to support
> * way, it's fine to back out this inlining logic
> */
> +#if defined(CONFIG_X86_64)
> insn_buf[0] = BPF_MOV32_IMM(BPF_REG_0, (u32)(unsigned long)&pcpu_hot.cpu_number);
> insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> insn_buf[2] = BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0);
> cnt = 3;
> +#elif defined(CONFIG_ARM64)
> + struct bpf_insn cpu_number_addr[2] = { BPF_LD_IMM64(BPF_REG_0, (u64)&cpu_number) };
>
this &cpu_number offset is not guaranteed to be within 4GB on arm64?
> + insn_buf[0] = cpu_number_addr[0];
> + insn_buf[1] = cpu_number_addr[1];
> + insn_buf[2] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
> + insn_buf[3] = BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0);
> + cnt = 4;
> +#endif
> new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
> if (!new_prog)
> return -ENOMEM;
> --
> 2.40.1
>
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