linux-kernel - Re: Comments on new user events ABI

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Date:   Tue, 29 Mar 2022 15:45:32 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Beau Belgrave <beaub@...ux.microsoft.com>,
        Beau Belgrave <beaub@...rosoft.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-trace-devel <linux-trace-devel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: Comments on new user events ABI

On Tue, 29 Mar 2022 09:25:52 -0700
Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:

> Thanks for flagging.
> 
> Whoever added this user_bpf* stuff please remove it immediately.
> It was never reviewed by bpf maintainers.

Heh, now you know how the x86 maintainers feel ;-)

> 
> It's a hard Nack to add a bpf interface to user_events.

Agreed, I'm thinking of marking the entire thing as broken such that it can
be worked on a bit more without a total revert (but still remove the BPF
portion on your request).

Beau, I agree with Mathieu, I don't think it's a good idea to expose the
"ftrace/perf/etc" users. The only thing that the application needs is a bit
to say "call the write now". And let the work be done within the kernel.
I think a single bit may be better, that way you can have many more events
on a page, and since they do not get modified often, it will be in hot
cache and fast.

-- Steve