From ede5acb7e03cf03782a13f597cce5c54be1c9232 Mon Sep 17 00:00:00 2001 From: Puranjay Mohan Date: Wed, 19 Jun 2024 13:13:34 +0000 Subject: [PATCH] bpf, arm64: inline bpf_get_current_task/_btf() helpers On ARM64, the pointer to task_struct is always available in the sp_el0 register and therefore the calls to bpf_get_current_task() and bpf_get_current_task_btf() can be inlined into a single MRS instruction. Here is the difference before and after this change: Before: ; struct task_struct *task = bpf_get_current_task_btf(); 54: mov x10, #0xffffffffffff7978 // #-34440 58: movk x10, #0x802b, lsl #16 5c: movk x10, #0x8000, lsl #32 60: blr x10 --------------> 0xffff8000802b7978 <+0>: mrs x0, sp_el0 64: add x7, x0, #0x0 <-------------- 0xffff8000802b797c <+4>: ret After: ; struct task_struct *task = bpf_get_current_task_btf(); 54: mrs x7, sp_el0 This shows around 1% performance improvement in artificial microbenchmark. Signed-off-by: Puranjay Mohan --- arch/arm64/net/bpf_jit_comp.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index 720336d288568..b838dab3bd263 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -1244,6 +1244,13 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, break; } + /* Implement helper call to bpf_get_current_task/_btf() inline */ + if (insn->src_reg == 0 && (insn->imm == BPF_FUNC_get_current_task || + insn->imm == BPF_FUNC_get_current_task_btf)) { + emit(A64_MRS_SP_EL0(r0), ctx); + break; + } + ret = bpf_jit_get_func_addr(ctx->prog, insn, extra_pass, &func_addr, &func_addr_fixed); if (ret < 0) @@ -2581,6 +2588,8 @@ bool bpf_jit_inlines_helper_call(s32 imm) { switch (imm) { case BPF_FUNC_get_smp_processor_id: + case BPF_FUNC_get_current_task: + case BPF_FUNC_get_current_task_btf: return true; default: return false;