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From: Jiri Olsa <jolsa@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
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 16:11:54 +0200	[thread overview]
Message-ID: <20201022141154.GB2332608@krava> (raw)
In-Reply-To: <20201022093510.37e8941f@gandalf.local.home>

On Thu, Oct 22, 2020 at 09:35:10AM -0400, Steven Rostedt wrote:
> On Thu, 22 Oct 2020 10:21:22 +0200
> Jiri Olsa <jolsa@kernel.org> wrote:
> 
> > hi,
> > this patchset tries to speed up the attach time for trampolines
> > and make bpftrace faster for wildcard use cases like:
> > 
> >   # bpftrace -ve "kfunc:__x64_sys_s* { printf("test\n"); }"
> > 
> > Profiles show mostly ftrace backend, because we add trampoline
> > functions one by one and ftrace direct function registering is
> > quite expensive. Thus main change in this patchset is to allow
> > batch attach and use just single ftrace call to attach or detach
> > multiple ips/trampolines.
> 
> The issue I have with this change is that the purpose of the direct
> trampoline was to give bpf access to the parameters of a function as if it
> was called directly. That is, it could see the parameters of a function
> quickly. I even made the direct function work if it wanted to also trace
> the return code.
> 
> What the direct calls is NOT, is a generic tracing function tracer. If that
> is required, then bpftrace should be registering itself with ftrace.
> If you are attaching to a set of functions, where it becomes obvious that
> its not being used to access specific parameters, then that's an abuse of
> the direct calls.
> 
> We already have one generic function tracer, we don't need another.

I understand direct calls as a way that bpf trampolines and ftrace can
co-exist together - ebpf trampolines need that functionality of accessing
parameters of a function as if it was called directly and at the same
point we need to be able attach to any function and to as many functions
as we want in a fast way

the bpftrace example above did not use arguments for simplicity, but they
could have been there ... I think we could detect arguments presence in
ebpf programs and use ftrace_ops directly in case they are not needed

jirka


  reply	other threads:[~2020-10-22 14:12 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 [this message]
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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