netdev - Re: [PATCH v2 bpf-next 2/7] tools/memory-model: add BPF ringbuf MPSC litmus tests

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Date:   Mon, 25 May 2020 20:05:35 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Jonathan Lemon <jonathan.lemon@...il.com>
Subject: Re: [PATCH v2 bpf-next 2/7] tools/memory-model: add BPF ringbuf MPSC
 litmus tests

On Mon, May 25, 2020 at 04:33:15PM -0700, Andrii Nakryiko wrote:
> On Fri, May 22, 2020 at 11:51 AM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
> >
> > On Thu, May 21, 2020 at 5:34 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> > >
> > > On Sun, May 17, 2020 at 12:57:22PM -0700, Andrii Nakryiko wrote:
> > > > Add 4 litmus tests for BPF ringbuf implementation, divided into two different
> > > > use cases.
> > > >
> > > > First, two unbounded case, one with 1 producer and another with
> > > > 2 producers, single consumer. All reservations are supposed to succeed.
> > > >
> > > > Second, bounded case with only 1 record allowed in ring buffer at any given
> > > > time. Here failures to reserve space are expected. Again, 1- and 2- producer
> > > > cases, single consumer, are validated.
> > > >
> > > > Just for the fun of it, I also wrote a 3-producer cases, it took *16 hours* to
> > > > validate, but came back successful as well. I'm not including it in this
> > > > patch, because it's not practical to run it. See output for all included
> > > > 4 cases and one 3-producer one with bounded use case.
> > > >
> > > > Each litmust test implements producer/consumer protocol for BPF ring buffer
> > > > implementation found in kernel/bpf/ringbuf.c. Due to limitations, all records
> > > > are assumed equal-sized and producer/consumer counters are incremented by 1.
> > > > This doesn't change the correctness of the algorithm, though.
> > >
> > > Very cool!!!
> > >
> > > However, these should go into Documentation/litmus-tests/bpf-rb or similar.
> > > Please take a look at Documentation/litmus-tests/ in -rcu, -tip, and
> > > -next, including the README file.
> > >
> > > The tools/memory-model/litmus-tests directory is for basic examples,
> > > not for the more complex real-world ones like these guys.  ;-)
> >
> > Oh, ok, I didn't realize there are more litmus tests under
> > Documentation/litmus-tests... Might have saved me some time (more
> > examples to learn from!) when I was writing mine :) Will check those
> > and move everything.
> 
> Ok, so Documentation/litmus-tests is not present in bpf-next, so I
> guess I'll have to split this patch out and post it separately. BTW,
> it's not in -rcu tree either, should I post this against linux-next
> tree directly?

It is on branch "dev" of -rcu, though yet not on branch "master".

							Thanx, Paul