[RFC 00/11] uprobes: Add support to optimize usdt probes on x86_64

[Jiri Olsa <jolsa@kernel.org>]

hi,
this patchset adds support to optimize usdt probes on top of 5-byte
nop instruction.

The generic approach (optimize all uprobes) is hard due to emulating
possible multiple original instructions and its related issues. The
usdt case, which stores 5-byte nop seems much easier, so starting
with that.

The basic idea is to replace breakpoint exception with syscall which
is faster on x86_64. For more details please see changelog of patch 7.

The first benchmark shows about 68% speed up (see below). The benchmark
triggers usdt probe in a loop and counts how many of those happened
per second.

It's still rfc state with some loose ends, but I'd be interested in
any feedback about the direction of this.

It's based on tip/perf/core with bpf-next/master merged on top of
that together with uprobe session patchset.

thanks,
jirka


current:
        # ./bench -w2 -d5 -a  trig-usdt
        Setting up benchmark 'trig-usdt'...
        Benchmark 'trig-usdt' started.
        Iter   0 ( 46.982us): hits    4.893M/s (  4.893M/prod), drops    0.000M/s, total operations    4.893M/s
        Iter   1 ( -5.967us): hits    4.892M/s (  4.892M/prod), drops    0.000M/s, total operations    4.892M/s
        Iter   2 ( -2.771us): hits    4.899M/s (  4.899M/prod), drops    0.000M/s, total operations    4.899M/s
        Iter   3 (  1.286us): hits    4.889M/s (  4.889M/prod), drops    0.000M/s, total operations    4.889M/s
        Iter   4 ( -2.871us): hits    4.881M/s (  4.881M/prod), drops    0.000M/s, total operations    4.881M/s
        Iter   5 (  1.005us): hits    4.886M/s (  4.886M/prod), drops    0.000M/s, total operations    4.886M/s
        Iter   6 ( 11.626us): hits    4.906M/s (  4.906M/prod), drops    0.000M/s, total operations    4.906M/s
        Iter   7 ( -6.638us): hits    4.896M/s (  4.896M/prod), drops    0.000M/s, total operations    4.896M/s
        Summary: hits    4.893 +- 0.009M/s (  4.893M/prod), drops    0.000 +- 0.000M/s, total operations    4.893 +- 0.009M/s

optimized:
        # ./bench -w2 -d5 -a  trig-usdt
        Setting up benchmark 'trig-usdt'...
        Benchmark 'trig-usdt' started.
        Iter   0 ( 46.073us): hits    8.258M/s (  8.258M/prod), drops    0.000M/s, total operations    8.258M/s
        Iter   1 ( -5.752us): hits    8.264M/s (  8.264M/prod), drops    0.000M/s, total operations    8.264M/s
        Iter   2 ( -1.333us): hits    8.263M/s (  8.263M/prod), drops    0.000M/s, total operations    8.263M/s
        Iter   3 ( -2.996us): hits    8.265M/s (  8.265M/prod), drops    0.000M/s, total operations    8.265M/s
        Iter   4 ( -0.620us): hits    8.264M/s (  8.264M/prod), drops    0.000M/s, total operations    8.264M/s
        Iter   5 ( -2.624us): hits    8.236M/s (  8.236M/prod), drops    0.000M/s, total operations    8.236M/s
        Iter   6 ( -0.840us): hits    8.232M/s (  8.232M/prod), drops    0.000M/s, total operations    8.232M/s
        Iter   7 ( -1.783us): hits    8.235M/s (  8.235M/prod), drops    0.000M/s, total operations    8.235M/s
        Summary: hits    8.249 +- 0.016M/s (  8.249M/prod), drops    0.000 +- 0.000M/s, total operations    8.249 +- 0.016M/s

---
Jiri Olsa (11):
      uprobes: Rename arch_uretprobe_trampoline function
      uprobes: Make copy_from_page global
      uprobes: Add len argument to uprobe_write_opcode
      uprobes: Add data argument to uprobe_write_opcode function
      uprobes: Add mapping for optimized uprobe trampolines
      uprobes: Add uprobe syscall to speed up uprobe
      uprobes/x86: Add support to optimize uprobes
      selftests/bpf: Use 5-byte nop for x86 usdt probes
      selftests/bpf: Add usdt trigger bench
      selftests/bpf: Add uprobe/usdt optimized test
      selftests/bpf: Add hit/attach/detach race optimized uprobe test

 arch/x86/entry/syscalls/syscall_64.tbl                    |   1 +
 arch/x86/include/asm/uprobes.h                            |   7 +++
 arch/x86/kernel/uprobes.c                                 | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 include/linux/syscalls.h                                  |   2 +
 include/linux/uprobes.h                                   |  25 +++++++++-
 kernel/events/uprobes.c                                   | 222 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------
 kernel/fork.c                                             |   2 +
 kernel/sys_ni.c                                           |   1 +
 tools/testing/selftests/bpf/bench.c                       |   2 +
 tools/testing/selftests/bpf/benchs/bench_trigger.c        |  45 +++++++++++++++++
 tools/testing/selftests/bpf/prog_tests/uprobe_optimized.c | 252 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/trigger_bench.c         |  10 +++-
 tools/testing/selftests/bpf/progs/uprobe_optimized.c      |  29 +++++++++++
 tools/testing/selftests/bpf/sdt.h                         |   9 +++-
 14 files changed, 768 insertions(+), 19 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/uprobe_optimized.c
 create mode 100644 tools/testing/selftests/bpf/progs/uprobe_optimized.c