[PATCH bpf-next v3 2/2] powerpc64/bpf: Inline bpf_get_smp_processor_id() and bpf_get_current_task/_btf()

[Saket Kumar Bhaskar <skb99@linux.ibm.com>]

Inline the calls to bpf_get_smp_processor_id() and bpf_get_current_task/_btf()
in the powerpc bpf jit.

powerpc saves the Logical processor number (paca_index) and pointer
to current task (__current) in paca.

Here is how the powerpc JITed assembly changes after this commit:

Before:

cpu = bpf_get_smp_processor_id();

addis 12, 2, -517
addi 12, 12, -29456
mtctr 12
bctrl
mr	8, 3

After:

cpu = bpf_get_smp_processor_id();

lhz 8, 8(13)

To evaluate the performance improvements introduced by this change,
the benchmark described in [1] was employed.

+---------------+-------------------+-------------------+--------------+
|      Name     |      Before       |        After      |   % change   |
|---------------+-------------------+-------------------+--------------|
| glob-arr-inc  | 40.701 ± 0.008M/s | 55.207 ± 0.021M/s |   + 35.64%   |
| arr-inc       | 39.401 ± 0.007M/s | 56.275 ± 0.023M/s |   + 42.42%   |
| hash-inc      | 24.944 ± 0.004M/s | 26.212 ± 0.003M/s |   +  5.08%   |
+---------------+-------------------+-------------------+--------------+

[1] https://github.com/anakryiko/linux/commit/8dec900975ef

Reviewed-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
---
 arch/powerpc/net/bpf_jit_comp.c   | 12 ++++++++++++
 arch/powerpc/net/bpf_jit_comp64.c | 11 +++++++++++
 2 files changed, 23 insertions(+)

diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index d53e9cd7563f..b243ee205885 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -471,6 +471,18 @@ bool bpf_jit_supports_percpu_insn(void)
 	return IS_ENABLED(CONFIG_PPC64);
 }
 
+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;
+	}
+}
+
 void *arch_alloc_bpf_trampoline(unsigned int size)
 {
 	return bpf_prog_pack_alloc(size, bpf_jit_fill_ill_insns);
diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 816f9d7d9e5d..76a44f9ad7d2 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -1399,6 +1399,17 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
 		case BPF_JMP | BPF_CALL:
 			ctx->seen |= SEEN_FUNC;
 
+			if (src_reg == bpf_to_ppc(BPF_REG_0)) {
+				if (imm == BPF_FUNC_get_smp_processor_id) {
+					EMIT(PPC_RAW_LHZ(src_reg, _R13, offsetof(struct paca_struct, paca_index)));
+					break;
+				} else if (imm == BPF_FUNC_get_current_task ||
+					   imm == BPF_FUNC_get_current_task_btf) {
+					EMIT(PPC_RAW_LD(src_reg, _R13, offsetof(struct paca_struct, __current)));
+					break;
+				}
+			}
+
 			ret = bpf_jit_get_func_addr(fp, &insn[i], extra_pass,
 						    &func_addr, &func_addr_fixed);
 			if (ret < 0)
-- 
2.51.0