[PATCH v4 0/5] powerpc/bpf: use BPF prog pack allocator

Hari Bathini hbathini at linux.ibm.com
Fri Sep 8 23:27:35 AEST 2023

Most BPF programs are small, but they consume a page each. For systems
with busy traffic and many BPF programs, this may also add significant
pressure on instruction TLB. High iTLB pressure usually slows down the
whole system causing visible performance degradation for production

bpf_prog_pack, a customized allocator that packs multiple bpf programs
into preallocated memory chunks, was proposed [1] to address it. This
series extends this support on powerpc.

Patches 1 & 2 add the arch specific functions needed to support this
feature. Patch 3 enables the support for powerpc and ensures cleanup
is handled gracefully. Patch 4 introduces patch_instructions() that
optimizes some calls while patching more than one instruction. Patch 5
leverages this new function to improve time taken for JIT'ing BPF

Note that the first 3 patches are sufficient to enable the support
for bpf_prog_pack on powerpc. Patches 4 & 5 are to improve the JIT
compilation time of BPF programs on powerpc.

Changes in v4:
* Updated bpf_patch_instructions() definition in patch 1/5 so that
  it doesn't have to be updated again in patch 2/5.
* Addressed Christophe's comment on bpf_arch_text_invalidate() return
  value in patch 2/5.

Changes in v3:
* Fixed segfault issue observed on ppc32 due to inaccurate offset
  calculation for branching.
* Tried to minimize the performance impact for patch_instruction()
  with the introduction of patch_instructions().
* Corrected uses of u32* vs ppc_instr_t.
* Moved the change that introduces patch_instructions() to after
  enabling bpf_prog_pack support.
* Added few comments to improve code readability.

[1] https://lore.kernel.org/bpf/20220204185742.271030-1-song@kernel.org/
[2] https://lore.kernel.org/all/20230309180028.180200-1-hbathini@linux.ibm.com/

Hari Bathini (5):
  powerpc/bpf: implement bpf_arch_text_copy
  powerpc/bpf: implement bpf_arch_text_invalidate for bpf_prog_pack
  powerpc/bpf: use bpf_jit_binary_pack_[alloc|finalize|free]
  powerpc/code-patching: introduce patch_instructions()
  powerpc/bpf: use patch_instructions()

 arch/powerpc/include/asm/code-patching.h |   1 +
 arch/powerpc/lib/code-patching.c         |  94 ++++++++++++---
 arch/powerpc/net/bpf_jit.h               |  12 +-
 arch/powerpc/net/bpf_jit_comp.c          | 144 ++++++++++++++++++-----
 arch/powerpc/net/bpf_jit_comp32.c        |  13 +-
 arch/powerpc/net/bpf_jit_comp64.c        |  10 +-
 6 files changed, 211 insertions(+), 63 deletions(-)


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