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From: Steven Rostedt <rostedt@goodmis.org>
To: Jiri Olsa <jolsa@redhat.com>
Cc: "Jiri Olsa" <jolsa@kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andriin@fb.com>,
	netdev@vger.kernel.org, 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>,
	"Jesper Brouer" <jbrouer@redhat.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Viktor Malik" <vmalik@redhat.com>
Subject: Re: [RFC bpf-next 00/16] bpf: Speed up trampoline attach
Date: Thu, 22 Oct 2020 12:21:50 -0400	[thread overview]
Message-ID: <20201022122150.45e81da0@gandalf.local.home> (raw)
In-Reply-To: <20201022104205.728dd135@gandalf.local.home>

On Thu, 22 Oct 2020 10:42:05 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> I'd like to see how batch functions will work. I guess I need to start
> looking at the bpf trampoline, to see if we can modify the ftrace
> trampoline to have a quick access to parameters. It would be much more
> beneficial to update the existing generic function tracer to have access to
> function parameters that all users could benefit from, than to tweak a
> single use case into giving this feature to a single user.

Looking at the creation of the bpf trampoline, I think I can modify ftrace
to have a more flexible callback. Something that passes the callback the
following:

 the function being traced.
 a pointer to the parent caller (that could be modified)
 a pointer to the original stack frame (what the stack was when the
      function is entered)
 An array of the arguments of the function (which could also be modified)

This is a change I've been wanting to make for some time, because it would
allow function graph to be a user of function tracer, and would give
everything access to the arguments.

We would still need a helper function to store all regs to keep kprobes
working unmodified, but this would still only be done if asked.

The above change shouldn't hurt performance for either ftrace or bpf
because it appears they both do the same. If BPF wants to have a batch
processing of functions, then I think we should modify ftrace to do this
new approach instead of creating another set of function trampolines.

-- Steve

  reply	other threads:[~2020-10-22 16:21 UTC|newest]

Thread overview: 51+ 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
2020-10-22  8:21 ` [RFC bpf-next 09/16] bpf: Add BPF_TRAMPOLINE_BATCH_ATTACH support Jiri Olsa
2020-10-22 11:55   ` kernel test robot
2020-10-22 11:57   ` kernel test robot
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 13:00   ` kernel test robot
2020-10-22 13:04   ` kernel test robot
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 [this message]
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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