On 6/19/2024 9:13 PM, Puranjay Mohan wrote:
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.
I think it would be better if more detailed data could be provided.
Signed-off-by: Puranjay Mohan <puranjay@xxxxxxxxxx>
---
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 720336d28856..b838dab3bd26 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;
Acked-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
