Re: [PATCHv3 perf/core 00/22] uprobes: Add support to optimize usdt probes on x86_64

[Jiri Olsa <olsajiri@gmail.com>]

ping

On Tue, Jun 17, 2025 at 03:08:08PM +0200, Jiri Olsa wrote:
> hi, ping
> 
> thanks,
> jirka
> 
> On Thu, Jun 05, 2025 at 03:23:27PM +0200, Jiri Olsa 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):
> > 
> > current:
> >         usermode-count :  152.501 ± 0.012M/s
> >         syscall-count  :   14.463 ± 0.062M/s
> > -->     uprobe-nop     :    3.160 ± 0.005M/s
> >         uprobe-push    :    3.003 ± 0.003M/s
> >         uprobe-ret     :    1.100 ± 0.003M/s
> >         uprobe-nop5    :    3.132 ± 0.012M/s
> >         uretprobe-nop  :    2.103 ± 0.002M/s
> >         uretprobe-push :    2.027 ± 0.004M/s
> >         uretprobe-ret  :    0.914 ± 0.002M/s
> >         uretprobe-nop5 :    2.115 ± 0.002M/s
> > 
> > after the change:
> >         usermode-count :  152.343 ± 0.400M/s
> >         syscall-count  :   14.851 ± 0.033M/s
> >         uprobe-nop     :    3.204 ± 0.005M/s
> >         uprobe-push    :    3.040 ± 0.005M/s
> >         uprobe-ret     :    1.098 ± 0.003M/s
> > -->     uprobe-nop5    :    7.286 ± 0.017M/s
> >         uretprobe-nop  :    2.144 ± 0.001M/s
> >         uretprobe-push :    2.069 ± 0.002M/s
> >         uretprobe-ret  :    0.922 ± 0.000M/s
> >         uretprobe-nop5 :    3.487 ± 0.001M/s
> > 
> > I see bit more speed up on Intel (above) compared to AMD. The big nop5
> > speed up is partly due to emulating nop5 and partly due to optimization.
> > 
> > The key speed up we do this for is the USDT switch from nop to nop5:
> > 	uprobe-nop     :    3.160 ± 0.005M/s
> > 	uprobe-nop5    :    7.286 ± 0.017M/s
> > 
> > 
> > Changes from v2:
> > - rebased on top of tip/master + mm/mm-stable + 1 extra change [1]
> > - added acks [Oleg,Andrii]
> > - more details changelog for patch 1 [Masami]
> > - several tests changes [Andrii]
> > - add explicit PAGE_SIZE low limit to vm_unmapped_area call [Andrii]
> > 
> > 
> > This patchset is adding new syscall, here are notes to check list items
> > in Documentation/process/adding-syscalls.rst:
> > 
> > - System Call Alternatives
> >   New syscall seems like the best way in here, because we need
> >   just to quickly enter kernel with no extra arguments processing,
> >   which we'd need to do if we decided to use another syscall.
> > 
> > - Designing the API: Planning for Extension
> >   The uprobe syscall is very specific and most likely won't be
> >   extended in the future.
> > 
> > - Designing the API: Other Considerations
> >   N/A because uprobe syscall does not return reference to kernel
> >   object.
> > 
> > - Proposing the API
> >   Wiring up of the uprobe system call is in separate change,
> >   selftests and man page changes are part of the patchset.
> > 
> > - Generic System Call Implementation
> >   There's no CONFIG option for the new functionality because it
> >   keeps the same behaviour from the user POV.
> > 
> > - x86 System Call Implementation
> >   It's 64-bit syscall only.
> > 
> > - Compatibility System Calls (Generic)
> >   N/A uprobe syscall has no arguments and is not supported
> >   for compat processes.
> > 
> > - Compatibility System Calls (x86)
> >   N/A uprobe syscall is not supported for compat processes.
> > 
> > - System Calls Returning Elsewhere
> >   N/A.
> > 
> > - Other Details
> >   N/A.
> > 
> > - Testing
> >   Adding new bpf selftests.
> > 
> > - Man Page
> >   Attached.
> > 
> > - Do not call System Calls in the Kernel
> >   N/A
> > 
> > pending todo (or follow ups):
> > - use PROCMAP_QUERY in tests
> > - alloc 'struct uprobes_state' for mm_struct only when needed [Andrii]
> > - use mm_cpumask(vma->vm_mm) in text_poke_sync
> > 
> > thanks,
> > jirka
> > 
> > 
> > Cc: Alejandro Colomar <alx@kernel.org>
> > Cc: Eyal Birger <eyal.birger@gmail.com>
> > Cc: kees@kernel.org
> > 
> > [1] https://lore.kernel.org/linux-trace-kernel/20250514101809.2010193-1-jolsa@kernel.org/T/#u
> > ---
> > Jiri Olsa (21):
> >       uprobes: Remove breakpoint in unapply_uprobe under mmap_write_lock
> >       uprobes: Rename arch_uretprobe_trampoline function
> >       uprobes: Make copy_from_page global
> >       uprobes: Add uprobe_write function
> >       uprobes: Add nbytes argument to uprobe_write
> >       uprobes: Add is_register argument to uprobe_write and uprobe_write_opcode
> >       uprobes: Add do_ref_ctr argument to uprobe_write function
> >       uprobes/x86: Add mapping for optimized uprobe trampolines
> >       uprobes/x86: Add uprobe syscall to speed up uprobe
> >       uprobes/x86: Add support to optimize uprobes
> >       selftests/bpf: Import usdt.h from libbpf/usdt project
> >       selftests/bpf: Reorg the uprobe_syscall test function
> >       selftests/bpf: Rename uprobe_syscall_executed prog to test_uretprobe_multi
> >       selftests/bpf: Add uprobe/usdt syscall tests
> >       selftests/bpf: Add hit/attach/detach race optimized uprobe test
> >       selftests/bpf: Add uprobe syscall sigill signal test
> >       selftests/bpf: Add optimized usdt variant for basic usdt test
> >       selftests/bpf: Add uprobe_regs_equal test
> >       selftests/bpf: Change test_uretprobe_regs_change for uprobe and uretprobe
> >       seccomp: passthrough uprobe systemcall without filtering
> >       selftests/seccomp: validate uprobe syscall passes through seccomp
> > 
> >  arch/arm/probes/uprobes/core.c                              |   2 +-
> >  arch/x86/entry/syscalls/syscall_64.tbl                      |   1 +
> >  arch/x86/include/asm/uprobes.h                              |   7 ++
> >  arch/x86/kernel/uprobes.c                                   | 525 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> >  include/linux/syscalls.h                                    |   2 +
> >  include/linux/uprobes.h                                     |  20 +++-
> >  kernel/events/uprobes.c                                     | 100 ++++++++++++-----
> >  kernel/fork.c                                               |   1 +
> >  kernel/seccomp.c                                            |  32 ++++--
> >  kernel/sys_ni.c                                             |   1 +
> >  tools/testing/selftests/bpf/prog_tests/uprobe_syscall.c     | 523 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++------
> >  tools/testing/selftests/bpf/prog_tests/usdt.c               |  38 ++++---
> >  tools/testing/selftests/bpf/progs/uprobe_syscall.c          |   4 +-
> >  tools/testing/selftests/bpf/progs/uprobe_syscall_executed.c |  60 +++++++++-
> >  tools/testing/selftests/bpf/test_kmods/bpf_testmod.c        |  11 +-
> >  tools/testing/selftests/bpf/usdt.h                          | 545 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  tools/testing/selftests/seccomp/seccomp_bpf.c               | 107 ++++++++++++++----
> >  17 files changed, 1867 insertions(+), 112 deletions(-)
> >  create mode 100644 tools/testing/selftests/bpf/usdt.h
> > 
> > 
> > Jiri Olsa (1):
> >       man2: Add uprobe syscall page
> > 
> >  man/man2/uprobe.2    |  1 +
> >  man/man2/uretprobe.2 | 36 ++++++++++++++++++++++++------------
> >  2 files changed, 25 insertions(+), 12 deletions(-)
> >  create mode 100644 man/man2/uprobe.2