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Date:   Wed, 26 Feb 2020 12:49:55 -0800
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
To:     Luigi Rizzo <lrizzo@google.com>
Cc:     Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>,
        linux-kernel@vger.kernel.org,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        naveen.n.rao@linux.ibm.com, ardb@kernel.org,
        Luigi Rizzo <rizzo@iet.unipi.it>,
        Paolo Abeni <pabeni@redhat.com>, giuseppe.lettieri@unipi.it,
        Jesper Dangaard Brouer <hawk@kernel.org>, mingo@redhat.com,
        acme@kernel.org, Steven Rostedt <rostedt@goodmis.org>,
        peterz@infradead.org
Subject: Re: [PATCH v3 0/2] kstats: kernel metric collector
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On Wed, Feb 26, 2020 at 09:26:22AM -0800, Luigi Rizzo wrote:
>   Any pointers to this are welcome; Alexei mentioned fentry/fexit and
>   bpf trampolines, but I haven't found an example that lets me do something
>   equivalent to kretprobe (take a timestamp before and one after a function
>   without explicit instrumentation)

please see the link in my previous email.

> - I still see some huge differences in usability, and this is in my opinion
>   one very big difference between the two approaches. The systems where data
>   collection may be of interest are not necessarily accessible to developers
>   with the skills to write custom bpf code,

bpf code and tooling is already written. There are bcc and bpftrace scripts
that already do what you're proposing without adding any new code to the kernel.
These tools are trivial to use. Requires zero knowledge in bpf.
So please stop the fud.