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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: "Jiri Olsa" <jolsa@redhat.com>, "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: Mon, 26 Oct 2020 21:30:14 -0700	[thread overview]
Message-ID: <20201027043014.ebzcbzospzsaptvu@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20201022104205.728dd135@gandalf.local.home>

On Thu, Oct 22, 2020 at 10:42:05AM -0400, Steven Rostedt wrote:
> On Thu, 22 Oct 2020 16:11:54 +0200
> Jiri Olsa <jolsa@redhat.com> wrote:
> 
> > 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
> 
> I was sold that bpf needed a quick and fast way to get the arguments of a
> function, as the only way to do that with ftrace is to save all registers,
> which, I was told was too much overhead, as if you only care about
> arguments, there's much less that is needed to save.
> 
> Direct calls wasn't added so that bpf and ftrace could co-exist, it was
> that for certain cases, bpf wanted a faster way to access arguments,
> because it still worked with ftrace, but the saving of regs was too
> strenuous.

Direct calls in ftrace were done so that ftrace and trampoline can co-exist.
There is no other use for it.

Jiri,
could you please redo your benchmarking hardcoding ftrace_managed=false ?
If going through register_ftrace_direct() is indeed so much slower
than arch_text_poke() then something gotta give.
Either register_ftrace_direct() has to become faster or users
have to give up on co-existing of bpf and ftrace.
So far not a single user cared about using trampoline and ftrace together.
So the latter is certainly an option.

Regardless, the patch 7 (rbtree of kallsyms) is probably good on its own.
Can you benchmark it independently and maybe resubmit if it's useful
without other patches?

  parent reply	other threads:[~2020-10-27  4:30 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
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 [this message]
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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