Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: > On Thu, Apr 25, 2024 at 3:14 AM Puranjay Mohan <puranjay@xxxxxxxxxx> wrote: >> >> Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes: >> >> > 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 nit: hmm, you are probably using a bit outdated bpftool, it should be 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) >> >> Yes, I was using the bpftool shipped with the distro. I tried it again >> with the latest bpftool and it emitted this as expected. > > Cool, would be nice to update the commit message with the right syntax > for next revision, thanks! > Sure, will do. >> >> > >> >> (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? >> >> If I remove this and later add support of percpu_insn on RISCV without >> inlining bpf_get_smp_processor_id() then it will cause problems here >> right? because then the last 5-6 lines inside this if(){} will be >> executed for RISCV. > > Just add > > #else > return -EFAULT; I don't think we can return. > #endif > > ? > > I'm trying to avoid this duplication of the defined(CONFIG_xxx) checks > for supported architectures. Does the following look correct? I will do it like this: /* 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 * 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) }; 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; #else goto next_insn; #endif new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt); if (!new_prog) return -ENOMEM; delta += cnt - 1; env->prog = prog = new_prog; insn = new_prog->insnsi + i + delta; goto next_insn; } >> >> > >> >> /* 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? >> >> Unfortunately, the per-cpu section is not placed in the first 4GB and >> therefore the per-cpu pointers are not 32-bit on ARM64. > > I see. It might make sense to turn x86-64 code into using MOV64_IMM as > well to keep more of the logic common. Then it will be just the > difference of an offset that's loaded. Give it a try? I think MOV64_IMM would have more overhead than MOV32_IMM and if we can use it in x86-64 we should keep doing it that way. Wdyt? >> >> > >> >> + 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 >> >>
