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Date: Fri, 26 Apr 2024 17:06:51 +0000
From: Puranjay Mohan <puranjay@...nel.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
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
Subject: Re: [PATCH bpf-next v3 2/2] bpf, arm64: inline
bpf_get_smp_processor_id() helper
Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
> 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
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
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