netdev - Re: [PATCH bpf-next v7 2/2] selftests/bpf: Selftest for real time helper

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Message-ID: <CANP3RGfyG9_vj5FkgJz2HV+8voLqP3N+6Qi5hpkqJntF0YSy-A@mail.gmail.com>
Date:   Mon, 5 Oct 2020 10:36:40 -0700
From:   Maciej Żenczykowski <maze@...gle.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     "Pujari, Bimmy" <bimmy.pujari@...el.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "kafai@...com" <kafai@...com>,
        "Nikravesh, Ashkan" <ashkan.nikravesh@...el.com>,
        "Alvarez, Daniel A" <daniel.a.alvarez@...el.com>
Subject: Re: [PATCH bpf-next v7 2/2] selftests/bpf: Selftest for real time helper

> Don't bother. This helper is no go.

I disagree on the 'no go' -- I do think we should have this helper.

The problem is it should only be used in some limited circumstances -
for example when processing packets coming in off the wire with real
times in them...  For example for something like measuring delay of
ntp frames.  This is of course testable but annoying (create a fake
ntp frame with gettimeofday injected timestamp in it, run it through
bpf, see what processing delay it reports).

Lets not make bpf even harder to use then it already is...