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bpf, arm64: inline bpf_get_smp_processor_id() helper

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Inline calls to bpf_get_smp_processor_id() helper in the JIT by emitting
a read from struct thread_info. The SP_EL0 system register holds the
pointer to the task_struct and thread_info is the first member of this
struct. We can read the cpu number from the thread_info.

Here is how the ARM64 JITed assembly changes after this commit:

                                      ARM64 JIT
                                     ===========

              BEFORE                                    AFTER
             --------                                  -------

int cpu = bpf_get_smp_processor_id();        int cpu = bpf_get_smp_processor_id();

mov     x10, #0xfffffffffffff4d0             mrs     x10, sp_el0
movk    x10, #0x802b, lsl #16                ldr     w7, [x10, #24]
movk    x10, #0x8000, lsl #32
blr     x10
add     x7, x0, #0x0

               Performance improvement using benchmark[1]

./benchs/run_bench_trigger.sh glob-arr-inc arr-inc hash-inc

+---------------+-------------------+-------------------+--------------+
|      Name     |      Before       |        After      |   % change   |
|---------------+-------------------+-------------------+--------------|
| glob-arr-inc  | 23.380 ± 1.675M/s | 25.893 ± 0.026M/s |   + 10.74%   |
| arr-inc       | 23.928 ± 0.034M/s | 25.213 ± 0.063M/s |   + 5.37%    |
| hash-inc      | 12.352 ± 0.005M/s | 12.609 ± 0.013M/s |   + 2.08%    |
+---------------+-------------------+-------------------+--------------+

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

Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240502151854.9810-5-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Puranjay Mohan
2024-05-02 15:18:54 +00:00
committed by Alexei Starovoitov
parent 7a4c32222b
commit 75fe4c0b3e
3 changed files with 28 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

1
arch/arm64/include/asm/insn.h
View File

@@ -138,6 +138,7 @@ enum aarch64_insn_special_register {
enum aarch64_insn_system_register {
AARCH64_INSN_SYSREG_TPIDR_EL1 = 0x4684,
AARCH64_INSN_SYSREG_TPIDR_EL2 = 0x6682,
AARCH64_INSN_SYSREG_SP_EL0 = 0x4208,
};
enum aarch64_insn_variant {

2
arch/arm64/net/bpf_jit.h
View File

@@ -302,5 +302,7 @@
aarch64_insn_gen_mrs(Rt, AARCH64_INSN_SYSREG_TPIDR_EL1)
#define A64_MRS_TPIDR_EL2(Rt) \
aarch64_insn_gen_mrs(Rt, AARCH64_INSN_SYSREG_TPIDR_EL2)
#define A64_MRS_SP_EL0(Rt) \
aarch64_insn_gen_mrs(Rt, AARCH64_INSN_SYSREG_SP_EL0)
#endif /* _BPF_JIT_H */

25
arch/arm64/net/bpf_jit_comp.c
View File

@@ -1228,6 +1228,21 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx,
const u8 r0 = bpf2a64[BPF_REG_0];
bool func_addr_fixed;
u64 func_addr;
u32 cpu_offset;
/* Implement helper call to bpf_get_smp_processor_id() inline */
if (insn->src_reg == 0 && insn->imm == BPF_FUNC_get_smp_processor_id) {
cpu_offset = offsetof(struct thread_info, cpu);
emit(A64_MRS_SP_EL0(tmp), ctx);
if (is_lsi_offset(cpu_offset, 2)) {
emit(A64_LDR32I(r0, tmp, cpu_offset), ctx);
} else {
emit_a64_mov_i(1, tmp2, cpu_offset, ctx);
emit(A64_LDR32(r0, tmp, tmp2), ctx);
}
break;
}
ret = bpf_jit_get_func_addr(ctx->prog, insn, extra_pass,
&func_addr, &func_addr_fixed);
@@ -2573,6 +2588,16 @@ bool bpf_jit_supports_percpu_insn(void)
return true;
}
bool bpf_jit_inlines_helper_call(s32 imm)
{
switch (imm) {
case BPF_FUNC_get_smp_processor_id:
return true;
default:
return false;
}
}
void bpf_jit_free(struct bpf_prog *prog)
{
if (prog->jited) {