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

Jiri Olsa
2024-12-11T13:34:08Z

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

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