Le 11/03/2025 à 17:09, Saket Kumar Bhaskar a écrit :
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With the introduction of commit 7bdbf7446305 ("bpf: add special
internal-only MOV instruction to resolve per-CPU addrs"),
a new BPF instruction BPF_MOV64_PERCPU_REG has been added to
resolve absolute addresses of per-CPU data from their per-CPU
offsets. This update requires enabling support for this
instruction in the powerpc JIT compiler.
As of commit 7a0268fa1a36 ("[PATCH] powerpc/64: per cpu data
optimisations"), the per-CPU data offset for the CPU is stored in
the paca.
To support this BPF instruction in the powerpc JIT, the following
powerpc instructions are emitted:
mr dst_reg, src_reg //Move src_reg to dst_reg, if src_reg != dst_reg
ld tmp1_reg, 48(13) //Load per-CPU data offset from paca(r13) in tmp1_reg.
add dst_reg, dst_reg, tmp1_reg //Add the per cpu offset to the dst.
Why not do:
add dst_reg, src_reg, tmp1_reg
instead of a combination of 'mr' and 'add' ?
To evaluate the performance improvements introduced by this change,
the benchmark described in [1] was employed.
Before Change:
glob-arr-inc : 41.580 ± 0.034M/s
arr-inc : 39.592 ± 0.055M/s
hash-inc : 25.873 ± 0.012M/s
After Change:
glob-arr-inc : 42.024 ± 0.049M/s
arr-inc : 55.447 ± 0.031M/s
hash-inc : 26.565 ± 0.014M/s
[1] https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fanakryiko%2Flinux%2Fcommit%2F8dec900975ef&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Ca4bc35a9cb49457fb5cc08dd60b73783%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638773062200197453%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=1t2Bc3w6Ye0u33UNEjsSAv114HDOGNXmk1I%2Fxt7K2sc%3D&reserved=0
Signed-off-by: Saket Kumar Bhaskar <skb99@xxxxxxxxxxxxx>
---
arch/powerpc/net/bpf_jit_comp.c | 5 +++++
arch/powerpc/net/bpf_jit_comp64.c | 8 ++++++++
2 files changed, 13 insertions(+)
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index 2991bb171a9b..3d4bd45a9a22 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -440,6 +440,11 @@ bool bpf_jit_supports_far_kfunc_call(void)
return IS_ENABLED(CONFIG_PPC64);
}
+bool bpf_jit_supports_percpu_insn(void)
+{
+ return true;
+}
+
What about PPC32 ?
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 233703b06d7c..06f06770ceea 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -679,6 +679,14 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32 *image, u32 *fimage, struct code
*/
case BPF_ALU | BPF_MOV | BPF_X: /* (u32) dst = src */
case BPF_ALU64 | BPF_MOV | BPF_X: /* dst = src */
+ if (insn_is_mov_percpu_addr(&insn[i])) {
+ if (dst_reg != src_reg)
+ EMIT(PPC_RAW_MR(dst_reg, src_reg));
Shouldn't be needed except for the non-SMP case maybe.
+#ifdef CONFIG_SMP
+ EMIT(PPC_RAW_LD(tmp1_reg, _R13, offsetof(struct paca_struct, data_offset)));
+ EMIT(PPC_RAW_ADD(dst_reg, dst_reg, tmp1_reg));
Can use src_reg as first operand instead of dst_reg
+#endif
data_offset always exists in paca_struct, please use
IS_ENABLED(CONFIG_SMP) instead of #ifdef
+ }
if (imm == 1) {
/* special mov32 for zext */
EMIT(PPC_RAW_RLWINM(dst_reg, dst_reg, 0, 0, 31));
--
2.43.5
