Re: [Bpf] Review of draft-thaler-bpf-isa-01

Watson Ladd <watsonbladd@gmail.com> Tue, 25 July 2023 18:37 UTC

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From: Watson Ladd <watsonbladd@gmail.com>
Date: Tue, 25 Jul 2023 11:36:48 -0700
Message-ID: <CACsn0cmf22zEN9AduiRiFnQ7XhY1ABRL=SwAwmmFgxJvVZAOsg@mail.gmail.com>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Dave Thaler <dthaler@microsoft.com>, "bpf@ietf.org" <bpf@ietf.org>, bpf <bpf@vger.kernel.org>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/bpf/iW-VpcP7VZp9i7RRLCTEZYoWL3M>
Subject: Re: [Bpf] Review of draft-thaler-bpf-isa-01
Precedence: list

On Tue, Jul 25, 2023 at 9:15 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Tue, Jul 25, 2023 at 7:03 AM Dave Thaler <dthaler@microsoft.com> wrote:
> >
> > I am forwarding the email below (after converting HTML to plain text)
> > to the mailto:bpf@vger.kernel.org list so replies can go to both lists.
> >
> > Please use this one for any replies.
> >
> > Thanks,
> > Dave
> >
> > > From: Bpf <bpf-bounces@ietf.org> On Behalf Of Watson Ladd
> > > Sent: Monday, July 24, 2023 10:05 PM
> > > To: bpf@ietf.org
> > > Subject: [Bpf] Review of draft-thaler-bpf-isa-01
> > >
> > > Dear BPF wg,
> > >
> > > I took a look at the draft and think it has some issues, unsurprisingly at this stage. One is
> > > the specification seems to use an underspecified C pseudo code for operations vs
> > > defining them mathematically.
>
> Hi Watson,
>
> This is not "underspecified C" pseudo code.
> This is assembly syntax parsed and emitted by GCC, LLVM, gas, Linux Kernel, etc.

I don't see a reference to any description of that in section 4.1.
It's possible I've overlooked this, and if people think this style of
definition is good enough that works for me. But I found table 4
pretty scanty on what exactly happens.
>
> > > The good news is I think this is very fixable although tedious.
> > >
> > > The other thornier issues are memory model etc. But the overall structure seems good
> > > and the document overall makes sense.
>
> What do you mean by "memory model" ?
> Do you see a reference to it ? Please be specific.

No, and that's the problem. Section 5.2 talks about atomic operations.
I'd expect that to be paired with a description of barriers so that
these work, or a big warning about when you need to use them. For
clarity I'm pretty unfamiliar with bpf as a technology, and it's
possible that with more knowledge this would make sense. On looking
back on that I don't even know if the memory space is flat, or
segmented: can I access maps through a value set to dst+offset, or
must I always used index? I'm just very confused.

Sincerely,
Watson

-- 
Astra mortemque praestare gradatim

[Bpf] Review of draft-thaler-bpf-isa-01 Watson Ladd
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Dave Thaler
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Dave Thaler
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Watson Ladd
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Will Hawkins
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Will Hawkins
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Will Hawkins
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Will Hawkins
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Will Hawkins
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Will Hawkins
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Dave Thaler
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Watson Ladd
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Alexei Starovoitov
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Dave Thaler
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Dave Thaler
Re: [Bpf] Review of draft-thaler-bpf-isa-01 David Vernet
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Watson Ladd
Re: [Bpf] Review of draft-thaler-bpf-isa-01 Will Hawkins
Re: [Bpf] Review of draft-thaler-bpf-isa-01 David Vernet
Re: [Bpf] Review of draft-thaler-bpf-isa-01 David Vernet