On Wed, Apr 24, 2024 at 10:36 AM Puranjay Mohan <puranjay@xxxxxxxxxx> 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 (bf) r0 = r0 nit: hmm, you are probably using a bit outdated bpftool, it should be emitted as: (bf) r0 = &(void __percpu *)(r0) 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@xxxxxxxxxx> > --- > kernel/bpf/verifier.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > Besides the nits, lgtm. Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > 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 >
