netdev - Re: [RFC PATCH 0/6] fprobe: Introduce fprobe function entry/exit probe

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Message-Id: <20220112163353.4da6a6b9c6eef69dbda50324@kernel.org>
Date:   Wed, 12 Jan 2022 16:33:53 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH 0/6] fprobe: Introduce fprobe function entry/exit
 probe

Hi Alexei,

On Tue, 11 Jan 2022 14:39:44 -0800
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> On Wed, Jan 12, 2022 at 12:00:17AM +0900, Masami Hiramatsu wrote:
> > Hi Jiri,
> > 
> > Here is a short series of patches, which shows what I replied
> > to your series.
> > 
> > This introduces the fprobe, the function entry/exit probe with
> > multiple probe point support. This also introduces the rethook
> > for hooking function return, which I cloned from kretprobe.
> > 
> > I also rewrite your [08/13] bpf patch to use this fprobe instead
> > of kprobes. I didn't tested that one, but the sample module seems
> > to work. Please test bpf part with your libbpf updates.
> > 
> > BTW, while implementing the fprobe, I introduced the per-probe
> > point private data, but I'm not sure why you need it. It seems
> > that data is not used from bpf...
> > 
> > If this is good for you, I would like to proceed this with
> > the rethook and rewrite the kretprobe to use the rethook to
> > hook the functions. That should be much cleaner (and easy to
> > prepare for the fgraph tracer integration)
> 
> What is the speed of attach/detach of thousands fprobes?

I've treaked my example module and it shows below result;

/lib/modules/5.16.0-rc4+/kernel/samples/fprobe # time insmod ./fprobe_example.ko
 symbol='btrfs_*'
[  187.095925] fprobe_init: 1028 symbols found
[  188.521694] fprobe_init: Planted fprobe at btrfs_*
real	0m 1.47s
user	0m 0.00s
sys	0m 1.36s

I think using ftrace_set_filter_ips() can make it faster.
(maybe it needs to drop per-probe point private data, that
prevents fprobe to use that interface)

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>