linux-kernel - Re: [PATCH bpf-next 0/4] fprobe: use rhashtable for fprobe_ip

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Message-ID: <aId3tjPnh_NyRLSv@krava>
Date: Mon, 28 Jul 2025 15:14:30 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: alexei.starovoitov@...il.com, mhiramat@...nel.org, rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com, hca@...ux.ibm.com,
	revest@...omium.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next 0/4] fprobe: use rhashtable for fprobe_ip_table

On Mon, Jul 28, 2025 at 12:12:47PM +0800, Menglong Dong wrote:
> For now, the budget of the hash table that is used for fprobe_ip_table is
> fixed, which is 256, and can cause huge overhead when the hooked functions
> is a huge quantity.
> 
> In this series, we use rhashtable for fprobe_ip_table to reduce the
> overhead.
> 
> Meanwhile, we also add the benchmark testcase "kprobe-multi-all", which
> will hook all the kernel functions during the testing. Before this series,
> the performance is:
>   usermode-count :  875.380 ± 0.366M/s 
>   kernel-count   :  435.924 ± 0.461M/s 
>   syscall-count  :   31.004 ± 0.017M/s 
>   fentry         :  134.076 ± 1.752M/s 
>   fexit          :   68.319 ± 0.055M/s 
>   fmodret        :   71.530 ± 0.032M/s 
>   rawtp          :  202.751 ± 0.138M/s 
>   tp             :   79.562 ± 0.084M/s 
>   kprobe         :   55.587 ± 0.028M/s 
>   kprobe-multi   :   56.481 ± 0.043M/s 
>   kprobe-multi-all:    6.283 ± 0.005M/s << look this
>   kretprobe      :   22.378 ± 0.028M/s 
>   kretprobe-multi:   28.205 ± 0.025M/s
> 
> With this series, the performance is:
>   usermode-count :  897.083 ± 5.347M/s 
>   kernel-count   :  431.638 ± 1.781M/s 
>   syscall-count  :   30.807 ± 0.057M/s 
>   fentry         :  134.803 ± 1.045M/s 
>   fexit          :   68.763 ± 0.018M/s 
>   fmodret        :   71.444 ± 0.052M/s 
>   rawtp          :  202.344 ± 0.149M/s 
>   tp             :   79.644 ± 0.376M/s 
>   kprobe         :   55.480 ± 0.108M/s 
>   kprobe-multi   :   57.302 ± 0.119M/s 
>   kprobe-multi-all:   57.855 ± 0.144M/s << look this

nice, so the we still trigger one function, but having all possible
functions attached, right?

thanks,
jirka


>   kretprobe      :   22.265 ± 0.023M/s 
>   kretprobe-multi:   27.740 ± 0.023M/s
> 
> The benchmark of "kprobe-multi-all" increase from 6.283M/s to 57.855M/s.
> 
> Menglong Dong (4):
>   fprobe: use rhashtable
>   selftests/bpf: move get_ksyms and get_addrs to trace_helpers.c
>   selftests/bpf: add benchmark testing for kprobe-multi-all
>   selftests/bpf: skip recursive functions for kprobe_multi
> 
>  include/linux/fprobe.h                        |   2 +-
>  kernel/trace/fprobe.c                         | 144 ++++++-----
>  tools/testing/selftests/bpf/bench.c           |   2 +
>  .../selftests/bpf/benchs/bench_trigger.c      |  30 +++
>  .../selftests/bpf/benchs/run_bench_trigger.sh |   2 +-
>  .../bpf/prog_tests/kprobe_multi_test.c        | 220 +----------------
>  tools/testing/selftests/bpf/trace_helpers.c   | 230 ++++++++++++++++++
>  tools/testing/selftests/bpf/trace_helpers.h   |   3 +
>  8 files changed, 351 insertions(+), 282 deletions(-)
> 
> -- 
> 2.50.1
> 
>