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Message-ID: <CAEf4BzaNM5H3Ad2=Syhhq1cbfuB5FrtuFTZHPTdQP3QME3naKA@mail.gmail.com>
Date: Fri, 26 Apr 2024 09:26:42 -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 v3 2/2] bpf, arm64: inline bpf_get_smp_processor_id()
helper
On Fri, Apr 26, 2024 at 5:14 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 = &(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>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> ---
> kernel/bpf/verifier.c | 24 +++++++++++++++++-------
> 1 file changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 4e474ef44e9c..6ff4e63b2ef2 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -20273,20 +20273,31 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> goto next_insn;
> }
>
> -#ifdef CONFIG_X86_64
> /* Implement bpf_get_smp_processor_id() inline. */
> if (insn->imm == BPF_FUNC_get_smp_processor_id &&
> prog->jit_requested && bpf_jit_supports_percpu_insn()) {
> /* BPF_FUNC_get_smp_processor_id inlining is an
> - * optimization, so if pcpu_hot.cpu_number is ever
> + * optimization, so if cpu_number_addr is ever
> * changed in some incompatible and hard to support
> * way, it's fine to back out this inlining logic
> */
> - 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;
> + u64 cpu_number_addr;
>
> +#if defined(CONFIG_X86_64)
> + cpu_number_addr = (u64)&pcpu_hot.cpu_number;
> +#elif defined(CONFIG_ARM64)
> + cpu_number_addr = (u64)&cpu_number;
> +#else
> + goto next_insn;
> +#endif
> + struct bpf_insn ld_cpu_number_addr[2] = {
> + BPF_LD_IMM64(BPF_REG_0, cpu_number_addr)
> + };
here we are violating C89 requirement to have a single block of
variable declarations by mixing variables and statements. I'm
surprised this is not triggering any build errors on !arm64 &&
!x86_64.
I think we can declare this BPF_LD_IMM64 instruction with zero "addr".
And then update
ld_cpu_number_addr[0].imm = (u32)cpu_number_addr;
ld_cpu_number_addr[1].imm = (u32)(cpu_number_addr >> 32);
WDYT?
nit: I'd rename ld_cpu_number_addr to ld_insn or something short like that
> + insn_buf[0] = ld_cpu_number_addr[0];
> + insn_buf[1] = ld_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;
nit: we normally have an empty line here to separate setting up
replacement instructions from actual patching
> new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
> if (!new_prog)
> return -ENOMEM;
> @@ -20296,7 +20307,6 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
> insn = new_prog->insnsi + i + delta;
> goto next_insn;
> }
> -#endif
> /* Implement bpf_get_func_arg inline. */
> if (prog_type == BPF_PROG_TYPE_TRACING &&
> insn->imm == BPF_FUNC_get_func_arg) {
> --
> 2.40.1
>
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