[PATCH bpf-next v3 0/3] bpf, arm64: use BPF prog pack allocator in BPF JIT

[Puranjay Mohan]

BPF programs currently consume a page each on ARM64. For systems with many BPF
programs, this adds significant pressure to instruction TLB. High iTLB pressure
usually causes slow down for the whole system.

Song Liu introduced the BPF prog pack allocator[1] to mitigate the above issue.
It packs multiple BPF programs into a single huge page. It is currently only
enabled for the x86_64 BPF JIT.

This patch series enables the BPF prog pack allocator for the ARM64 BPF JIT.

====================================================
Performance Analysis of prog pack allocator on ARM64
====================================================

To test the performance of the BPF prog pack allocator on ARM64, a stresser
tool[2] was built. This tool loads 8 BPF programs on the system and triggers
5 of them in an infinite loop by doing system calls.

The runner script starts 20 instances of the above which loads 8*20=160 BPF
programs on the system, 5*20=100 of which are being constantly triggered.

In the above environment we try to build Python-3.8.4 and try to find different
iTLB metrics for the compilation done by gcc-12.2.0.

The source code[3] is  configured with the following command:
./configure --enable-optimizations --with-ensurepip=install

Then the runner script is executed with the following command:
./run.sh "perf stat -e ITLB_WALK,L1I_TLB,INST_RETIRED,iTLB-load-misses -a make -j32"

This builds Python while 160 BPF programs are loaded and 100 are being constantly
triggered and measures iTLB related metrics.

The output of the above command is discussed below before and after enabling the
BPF prog pack allocator.

The tests were run on qemu-system-aarch64 with 32 cpus, 4G memory, -machine virt,
-cpu host, and -enable-kvm.

Results
-------

Before enabling prog pack allocator:
------------------------------------

Performance counter stats for 'system wide':

         333278635      ITLB_WALK
     6762692976558      L1I_TLB
    25359571423901      INST_RETIRED
       15824054789      iTLB-load-misses

     189.029769053 seconds time elapsed

After enabling prog pack allocator:
-----------------------------------

Performance counter stats for 'system wide':

         190333544      ITLB_WALK
     6712712386528      L1I_TLB
    25278233304411      INST_RETIRED
        5716757866      iTLB-load-misses

     185.392650561 seconds time elapsed

Improvements in metrics
-----------------------

Compilation time                             ---> 1.92% faster
iTLB-load-misses/Sec (Less is better)        ---> 63.16% decrease
ITLB_WALK/1000 INST_RETIRED (Less is better) ---> 42.71% decrease
ITLB_Walk/L1I_TLB (Less is better)           ---> 42.47% decrease

[1] https://lore.kernel.org/bpf/20220204185742.271030-1-song@kernel.org/
[2] https://github.com/puranjaymohan/BPF-Allocator-Bench
[3] https://www.python.org/ftp/python/3.8.4/Python-3.8.4.tgz

Chanes in V2 => V3: Changes only in 3rd patch
1. Set prog = orig_prog; in the failure path of bpf_jit_binary_pack_finalize()
call.
2. Add comments explaining the usage of the offsets in the exception table.

Changes in v1 => v2:
1. Make the naming consistent in the 3rd patch:
   ro_image and image
   ro_header and header
   ro_image_ptr and image_ptr
2. Use names dst/src in place of addr/opcode in second patch.
3. Add Acked-by: Song Liu <song at kernel.org> in 1st and 2nd patch.

Puranjay Mohan (3):
  bpf: make bpf_prog_pack allocator portable
  arm64: patching: Add aarch64_insn_copy()
  bpf, arm64: use bpf_jit_binary_pack_alloc

 arch/arm64/include/asm/patching.h |   1 +
 arch/arm64/kernel/patching.c      |  39 +++++++++
 arch/arm64/net/bpf_jit_comp.c     | 138 +++++++++++++++++++++++++-----
 kernel/bpf/core.c                 |   8 +-
 4 files changed, 159 insertions(+), 27 deletions(-)

-- 
2.40.1