Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > On Fri, Apr 26, 2024 at 5:14 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 = &(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> >> Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> >> --- >> 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 I agree with you, What do you think about the following diff: --- 8< --- -#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; + struct bpf_insn ld_insn[2] = { + BPF_LD_IMM64(BPF_REG_0, 0) + }; + +#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 + ld_insn[0].imm = (u32)cpu_number_addr; + ld_insn[1].imm = (u32)(cpu_number_addr >> 32); + insn_buf[0] = ld_insn[0]; + insn_buf[1] = ld_insn[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; new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt); if (!new_prog) @@ -20296,7 +20310,6 @@ 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. */ --- >8--- Thanks, Puranjay
