Re: [PATCH bpf-next 00/13] uprobes: Add support to optimize usdt probes on x86_64

[Andrii Nakryiko]

On Wed, Dec 11, 2024 at 5:34 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
>
> 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 8.
>
> The run_bench_uprobes.sh benchmark triggers uprobe (on top of different
> original instructions) in a loop and counts how many of those happened
> per second (the unit below is million loops).
>
> There's big speed up if you consider current usdt implementation
> (uprobe-nop) compared to proposed usdt (uprobe-nop5):
>
>   # ./benchs/run_bench_uprobes.sh
>
>       usermode-count :  233.831 ± 0.257M/s
>       syscall-count  :   12.107 ± 0.038M/s
>   --> uprobe-nop     :    3.246 ± 0.004M/s
>       uprobe-push    :    3.057 ± 0.000M/s
>       uprobe-ret     :    1.113 ± 0.003M/s
>   --> uprobe-nop5    :    6.751 ± 0.037M/s
>       uretprobe-nop  :    1.740 ± 0.015M/s
>       uretprobe-push :    1.677 ± 0.018M/s
>       uretprobe-ret  :    0.852 ± 0.005M/s
>       uretprobe-nop5 :    6.769 ± 0.040M/s

uretprobe-nop5 throughput is the same as uprobe-nop5?..


>
>
> v1 changes:
> - rebased on top of bpf-next/master
> - couple of function/variable renames [Andrii]
> - added nop5 emulation [Andrii]
> - added checks to arch_uprobe_verify_opcode [Andrii]
> - fixed arch_uprobe_is_callable/find_nearest_page [Andrii]
> - used CALL_INSN_OPCODE [Masami]
> - added uprobe-nop5 benchmark [Andrii]
> - using atomic64_t in tramp_area [Andri]
> - using single page for all uprobe trampoline mappings
>
> thanks,
> jirka
>
>
> ---
> Jiri Olsa (13):
>       uprobes: Rename arch_uretprobe_trampoline function
>       uprobes: Make copy_from_page global
>       uprobes: Add nbytes argument to uprobe_write_opcode
>       uprobes: Add arch_uprobe_verify_opcode function
>       uprobes: Add mapping for optimized uprobe trampolines
>       uprobes/x86: Add uprobe syscall to speed up uprobe
>       uprobes/x86: Add support to emulate nop5 instruction
>       uprobes/x86: Add support to optimize uprobes
>       selftests/bpf: Use 5-byte nop for x86 usdt probes
>       selftests/bpf: Add uprobe/usdt optimized test
>       selftests/bpf: Add hit/attach/detach race optimized uprobe test
>       selftests/bpf: Add uprobe syscall sigill signal test
>       selftests/bpf: Add 5-byte nop uprobe trigger bench
>
>  arch/x86/entry/syscalls/syscall_64.tbl                  |   1 +
>  arch/x86/include/asm/uprobes.h                          |   7 +++
>  arch/x86/kernel/uprobes.c                               | 255 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/syscalls.h                                |   2 +
>  include/linux/uprobes.h                                 |  25 +++++++-
>  kernel/events/uprobes.c                                 | 191 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  kernel/fork.c                                           |   1 +
>  kernel/sys_ni.c                                         |   1 +
>  tools/testing/selftests/bpf/bench.c                     |  12 ++++
>  tools/testing/selftests/bpf/benchs/bench_trigger.c      |  42 +++++++++++++
>  tools/testing/selftests/bpf/benchs/run_bench_uprobes.sh |   2 +-
>  tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c | 326 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  tools/testing/selftests/bpf/progs/uprobe_optimized.c    |  29 +++++++++
>  tools/testing/selftests/bpf/sdt.h                       |   9 ++-
>  14 files changed, 880 insertions(+), 23 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/uprobe_optimized.c