From: Jiri Olsa <jolsa@redhat.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" <andriin@fb.com>,
Networking <netdev@vger.kernel.org>, bpf <bpf@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>, "Daniel Xu" <dxu@dxuuu.xyz>,
"Steven Rostedt" <rostedt@goodmis.org>,
"Jesper Brouer" <jbrouer@redhat.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
"Viktor Malik" <vmalik@redhat.com>
Subject: Re: [RFC bpf-next 08/16] bpf: Use delayed link free in bpf_link_put
Date: Sun, 25 Oct 2020 20:02:14 +0100 [thread overview]
Message-ID: <20201025190214.GB2681365@krava> (raw)
In-Reply-To: <CAEf4BzZ9zwA=SrLTx9JT50OeM6fVPg0Py0Gx+K9ah2we8YtCRA@mail.gmail.com>
On Fri, Oct 23, 2020 at 12:46:15PM -0700, Andrii Nakryiko wrote:
> On Thu, Oct 22, 2020 at 8:01 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Moving bpf_link_free call into delayed processing so we don't
> > need to wait for it when releasing the link.
> >
> > For example bpf_tracing_link_release could take considerable
> > amount of time in bpf_trampoline_put function due to
> > synchronize_rcu_tasks call.
> >
> > It speeds up bpftrace release time in following example:
> >
> > Before:
> >
> > Performance counter stats for './src/bpftrace -ve kfunc:__x64_sys_s*
> > { printf("test\n"); } i:ms:10 { printf("exit\n"); exit();}' (5 runs):
> >
> > 3,290,457,628 cycles:k ( +- 0.27% )
> > 933,581,973 cycles:u ( +- 0.20% )
> >
> > 50.25 +- 4.79 seconds time elapsed ( +- 9.53% )
> >
> > After:
> >
> > Performance counter stats for './src/bpftrace -ve kfunc:__x64_sys_s*
> > { printf("test\n"); } i:ms:10 { printf("exit\n"); exit();}' (5 runs):
> >
> > 2,535,458,767 cycles:k ( +- 0.55% )
> > 940,046,382 cycles:u ( +- 0.27% )
> >
> > 33.60 +- 3.27 seconds time elapsed ( +- 9.73% )
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > kernel/bpf/syscall.c | 8 ++------
> > 1 file changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index 1110ecd7d1f3..61ef29f9177d 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -2346,12 +2346,8 @@ void bpf_link_put(struct bpf_link *link)
> > if (!atomic64_dec_and_test(&link->refcnt))
> > return;
> >
> > - if (in_atomic()) {
> > - INIT_WORK(&link->work, bpf_link_put_deferred);
> > - schedule_work(&link->work);
> > - } else {
> > - bpf_link_free(link);
> > - }
> > + INIT_WORK(&link->work, bpf_link_put_deferred);
> > + schedule_work(&link->work);
>
> We just recently reverted this exact change. Doing this makes it
> non-deterministic from user-space POV when the BPF program is
> **actually** detached. This makes user-space programming much more
> complicated and unpredictable. So please don't do this. Let's find
> some other way to speed this up.
ok, makes sense
jirka
>
> > }
> >
> > static int bpf_link_release(struct inode *inode, struct file *filp)
> > --
> > 2.26.2
> >
>
next prev parent reply other threads:[~2020-10-25 19:02 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-22 8:21 [RFC bpf-next 00/16] bpf: Speed up trampoline attach Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 01/16] ftrace: Add check_direct_entry function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 02/16] ftrace: Add adjust_direct_size function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 03/16] ftrace: Add get/put_direct_func function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 04/16] ftrace: Add ftrace_set_filter_ips function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 05/16] ftrace: Add register_ftrace_direct_ips function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 06/16] ftrace: Add unregister_ftrace_direct_ips function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 07/16] kallsyms: Use rb tree for kallsyms name search Jiri Olsa
2020-10-28 18:25 ` Jiri Olsa
2020-10-28 21:15 ` Alexei Starovoitov
2020-10-29 9:29 ` Jiri Olsa
2020-10-29 22:45 ` Andrii Nakryiko
2020-10-28 22:40 ` Andrii Nakryiko
2020-10-29 9:33 ` Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 08/16] bpf: Use delayed link free in bpf_link_put Jiri Olsa
2020-10-23 19:46 ` Andrii Nakryiko
2020-10-25 19:02 ` Jiri Olsa [this message]
2020-10-22 8:21 ` [RFC bpf-next 09/16] bpf: Add BPF_TRAMPOLINE_BATCH_ATTACH support Jiri Olsa
2020-10-23 20:03 ` Andrii Nakryiko
2020-10-23 20:31 ` Steven Rostedt
2020-10-23 22:23 ` Andrii Nakryiko
2020-10-25 19:41 ` Jiri Olsa
2020-10-26 23:19 ` Andrii Nakryiko
2020-10-22 8:21 ` [RFC bpf-next 10/16] bpf: Add BPF_TRAMPOLINE_BATCH_DETACH support Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 11/16] bpf: Sync uapi bpf.h to tools Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 12/16] bpf: Move synchronize_rcu_mult for batch processing (NOT TO BE MERGED) Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 13/16] libbpf: Add trampoline batch attach support Jiri Olsa
2020-10-23 20:09 ` Andrii Nakryiko
2020-10-25 19:11 ` Jiri Olsa
2020-10-26 23:15 ` Andrii Nakryiko
2020-10-27 19:03 ` Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 14/16] libbpf: Add trampoline batch detach support Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 15/16] selftests/bpf: Add trampoline batch test Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 16/16] selftests/bpf: Add attach batch test (NOT TO BE MERGED) Jiri Olsa
2020-10-22 13:35 ` [RFC bpf-next 00/16] bpf: Speed up trampoline attach Steven Rostedt
2020-10-22 14:11 ` Jiri Olsa
2020-10-22 14:42 ` Steven Rostedt
2020-10-22 16:21 ` Steven Rostedt
2020-10-22 20:52 ` Steven Rostedt
2020-10-23 6:09 ` Jiri Olsa
2020-10-23 13:50 ` Steven Rostedt
2020-10-25 19:01 ` Jiri Olsa
2020-10-27 4:30 ` Alexei Starovoitov
2020-10-27 13:14 ` Steven Rostedt
2020-10-27 14:28 ` Jiri Olsa
2020-10-28 21:13 ` Alexei Starovoitov
2020-10-29 11:09 ` Jiri Olsa
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