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

Andrii Nakryiko
2024-12-13T00:43:14Z

On Wed, Dec 11, 2024 at 5:34 AM Jiri Olsa <jolsa@kernel.org> 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