[PATCH bpf-next v3 0/4] fprobe: use rhashtable for fprobe_ip_table

[Menglong Dong]

For now, the budget of the hash table that is used for fprobe_ip_table is
fixed, which is 256, and can cause huge overhead when the hooked functions
is a huge quantity.

In this series, we use rhltable for fprobe_ip_table to reduce the
overhead.

Meanwhile, we also add the benchmark testcase "kprobe-multi-all" and, which
will hook all the kernel functions during the testing. Before this series,
the performance is:
  usermode-count :  889.269 ± 0.053M/s 
  kernel-count   :  437.149 ± 0.501M/s 
  syscall-count  :   31.618 ± 0.725M/s 
  fentry         :  135.591 ± 0.129M/s 
  fexit          :   68.127 ± 0.062M/s 
  fmodret        :   71.764 ± 0.098M/s 
  rawtp          :  198.375 ± 0.190M/s 
  tp             :   79.770 ± 0.064M/s 
  kprobe         :   54.590 ± 0.021M/s 
  kprobe-multi   :   57.940 ± 0.044M/s 
  kprobe-multi-all:   12.151 ± 0.020M/s 
  kretprobe      :   21.945 ± 0.163M/s 
  kretprobe-multi:   28.199 ± 0.018M/s 
  kretprobe-multi-all:    9.667 ± 0.008M/s

With this series, the performance is:
  usermode-count :  888.863 ± 0.378M/s 
  kernel-count   :  429.339 ± 0.136M/s 
  syscall-count  :   31.215 ± 0.019M/s 
  fentry         :  135.604 ± 0.118M/s 
  fexit          :   68.470 ± 0.074M/s 
  fmodret        :   70.957 ± 0.016M/s 
  rawtp          :  202.650 ± 0.304M/s 
  tp             :   80.428 ± 0.053M/s 
  kprobe         :   55.915 ± 0.074M/s 
  kprobe-multi   :   54.015 ± 0.039M/s 
  kprobe-multi-all:   46.381 ± 0.024M/s 
  kretprobe      :   22.234 ± 0.050M/s 
  kretprobe-multi:   27.946 ± 0.016M/s 
  kretprobe-multi-all:   24.439 ± 0.016M/s

The benchmark of "kprobe-multi-all" increase from 12.151M/s to 46.381M/s.

I don't know why, but the benchmark result for "kprobe-multi-all" is much
better in this version for the legacy case(without this series). In V2,
the benchmark increase from 6.283M/s to 54.487M/s, but it become
12.151M/s to 46.381M/s in this version. Maybe it has some relation with
the compiler optimization :/

The result of this version should be more accurate, which is similar to
Jiri's result: from 3.565 ± 0.047M/s to 11.553 ± 0.458M/s.

The locking is not handled properly in the first patch. In the
fprobe_entry, we should use RCU when we access the rhlist_head. However,
we can't use RCU for __fprobe_handler, as it can sleep. In the origin
logic, it seems that the usage of hlist_for_each_entry_from_rcu() is not
protected by rcu_read_lock neither, isn't it? I don't know how to handle
this part ;(

Changes since V2:

* some format optimization, and handle the error that returned from
  rhltable_insert in insert_fprobe_node for the 1st patch
* add "kretprobe-multi-all" testcase to the 4th patch
* attach a empty kprobe-multi prog to the kernel functions, which don't
  call incr_count(), to make the result more accurate in the 4th patch

Changes Since V1:

* use rhltable instead of rhashtable to handle the duplicate key.

Menglong Dong (4):
  fprobe: use rhltable for fprobe_ip_table
  selftests/bpf: move get_ksyms and get_addrs to trace_helpers.c
  selftests/bpf: skip recursive functions for kprobe_multi
  selftests/bpf: add benchmark testing for kprobe-multi-all

 include/linux/fprobe.h                        |   2 +-
 kernel/trace/fprobe.c                         | 155 +++++++-----
 tools/testing/selftests/bpf/bench.c           |   4 +
 .../selftests/bpf/benchs/bench_trigger.c      |  54 ++++
 .../selftests/bpf/benchs/run_bench_trigger.sh |   4 +-
 .../bpf/prog_tests/kprobe_multi_test.c        | 220 +----------------
 .../selftests/bpf/progs/trigger_bench.c       |  12 +
 tools/testing/selftests/bpf/trace_helpers.c   | 233 ++++++++++++++++++
 tools/testing/selftests/bpf/trace_helpers.h   |   3 +
 9 files changed, 401 insertions(+), 286 deletions(-)

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2.50.1