From: Jiri Olsa <olsajiri@gmail.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>
Subject: Re: [RFC bpf-next 3/4] bpf: Resolve symbols with kallsyms_lookup_names for kprobe multi link
Date: Tue, 12 Apr 2022 20:42:11 +0200 [thread overview]
Message-ID: <YlXIA12sLNUOc+nm@krava> (raw)
In-Reply-To: <CAEf4BzYrRSB2wSYVmMCGA80RY6Hy2Chtt3MnXFy7+-Feh+2FBw@mail.gmail.com>
On Mon, Apr 11, 2022 at 03:15:32PM -0700, Andrii Nakryiko wrote:
> On Thu, Apr 7, 2022 at 5:53 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Using kallsyms_lookup_names function to speed up symbols lookup in
> > kprobe multi link attachment and replacing with it the current
> > kprobe_multi_resolve_syms function.
> >
> > This speeds up bpftrace kprobe attachment:
> >
> > # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* { } i:ms:1 { exit(); }'
> > ...
> > 6.5681 +- 0.0225 seconds time elapsed ( +- 0.34% )
> >
> > After:
> >
> > # perf stat -r 5 -e cycles ./src/bpftrace -e 'kprobe:x* { } i:ms:1 { exit(); }'
> > ...
> > 0.5661 +- 0.0275 seconds time elapsed ( +- 4.85% )
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > kernel/trace/bpf_trace.c | 123 +++++++++++++++++++++++----------------
> > 1 file changed, 73 insertions(+), 50 deletions(-)
> >
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index b26f3da943de..2602957225ba 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -2226,6 +2226,72 @@ struct bpf_kprobe_multi_run_ctx {
> > unsigned long entry_ip;
> > };
> >
> > +struct user_syms {
> > + const char **syms;
> > + char *buf;
> > +};
> > +
> > +static int copy_user_syms(struct user_syms *us, void __user *usyms, u32 cnt)
> > +{
> > + const char __user **usyms_copy = NULL;
> > + const char **syms = NULL;
> > + char *buf = NULL, *p;
> > + int err = -EFAULT;
> > + unsigned int i;
> > + size_t size;
> > +
> > + size = cnt * sizeof(*usyms_copy);
> > +
> > + usyms_copy = kvmalloc(size, GFP_KERNEL);
> > + if (!usyms_copy)
> > + return -ENOMEM;
>
> do you really need usyms_copy? why not just read one pointer at a time?
>
> > +
> > + if (copy_from_user(usyms_copy, usyms, size))
> > + goto error;
> > +
> > + err = -ENOMEM;
> > + syms = kvmalloc(size, GFP_KERNEL);
> > + if (!syms)
> > + goto error;
> > +
> > + /* TODO this potentially allocates lot of memory (~6MB in my tests
> > + * with attaching ~40k functions). I haven't seen this to fail yet,
> > + * but it could be changed to allocate memory gradually if needed.
> > + */
> > + size = cnt * KSYM_NAME_LEN;
>
> this reassignment of size is making it hard to follow the code, you
> can just do cnt * KSYM_NAME_LEN inside kvmalloc, you don't ever use it
> anywhere else
ok
>
> > + buf = kvmalloc(size, GFP_KERNEL);
> > + if (!buf)
> > + goto error;
> > +
> > + for (p = buf, i = 0; i < cnt; i++) {
>
> like here, before doing strncpy_from_user() you can read usyms[i] from
> user-space into temporary variable, no need for extra kvmalloc?
yes, that could work.. one copy_from_user seemed faster than separate
get_user calls, but then it's without memory allocation.. so perhaps
that's better
jirka
>
> > + err = strncpy_from_user(p, usyms_copy[i], KSYM_NAME_LEN);
> > + if (err == KSYM_NAME_LEN)
> > + err = -E2BIG;
> > + if (err < 0)
> > + goto error;
> > + syms[i] = p;
> > + p += err + 1;
> > + }
> > +
> > + err = 0;
> > + us->syms = syms;
> > + us->buf = buf;
> > +
>
> [...]
next prev parent reply other threads:[~2022-04-12 18:42 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-07 12:52 [RFC bpf-next 0/4] bpf: Speed up symbol resolving in kprobe multi link Jiri Olsa
2022-04-07 12:52 ` [RFC bpf-next 1/4] kallsyms: Add kallsyms_lookup_names function Jiri Olsa
2022-04-08 0:57 ` Masami Hiramatsu
2022-04-13 7:27 ` Jiri Olsa
2022-04-08 23:19 ` Alexei Starovoitov
2022-04-09 20:24 ` Jiri Olsa
2022-04-12 20:46 ` Jiri Olsa
2022-04-15 0:47 ` Masami Hiramatsu
2022-04-15 22:39 ` Jiri Olsa
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-12 20:28 ` Jiri Olsa
2022-04-07 12:52 ` [RFC bpf-next 2/4] fprobe: Resolve symbols with kallsyms_lookup_names Jiri Olsa
2022-04-08 0:58 ` Masami Hiramatsu
2022-04-07 12:52 ` [RFC bpf-next 3/4] bpf: Resolve symbols with kallsyms_lookup_names for kprobe multi link Jiri Olsa
2022-04-08 23:26 ` Alexei Starovoitov
2022-04-09 20:24 ` Jiri Olsa
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-12 18:42 ` Jiri Olsa [this message]
2022-04-07 12:52 ` [RFC bpf-next 4/4] selftests/bpf: Add attach bench test Jiri Olsa
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-12 0:49 ` Masami Hiramatsu
2022-04-12 22:51 ` Andrii Nakryiko
2022-04-16 14:21 ` Masami Hiramatsu
2022-04-18 17:33 ` Steven Rostedt
2022-04-28 13:58 ` Steven Rostedt
2022-04-28 13:59 ` Steven Rostedt
2022-04-28 18:59 ` Alexei Starovoitov
2022-04-28 20:05 ` Steven Rostedt
2022-04-28 23:32 ` Andrii Nakryiko
2022-04-28 23:53 ` Steven Rostedt
2022-04-29 0:09 ` Steven Rostedt
2022-04-29 0:31 ` Steven Rostedt
2022-04-13 16:44 ` Steven Rostedt
2022-04-13 16:45 ` Andrii Nakryiko
2022-04-13 16:59 ` Steven Rostedt
2022-04-13 19:02 ` Andrii Nakryiko
2022-04-12 15:44 ` Jiri Olsa
2022-04-12 22:59 ` Andrii Nakryiko
2022-04-08 23:29 ` [RFC bpf-next 0/4] bpf: Speed up symbol resolving in kprobe multi link Alexei Starovoitov
2022-04-09 20:24 ` Jiri Olsa
2022-04-11 22:15 ` Andrii Nakryiko
2022-04-11 22:18 ` Alexei Starovoitov
2022-04-11 22:21 ` Andrii Nakryiko
2022-04-12 15:46 ` Jiri Olsa
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