From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 12302 invoked from network); 3 Sep 2021 17:48:15 -0000 Received: from minnie.tuhs.org (45.79.103.53) by inbox.vuxu.org with ESMTPUTF8; 3 Sep 2021 17:48:15 -0000 Received: by minnie.tuhs.org (Postfix, from userid 112) id 5A0069C8BB; Sat, 4 Sep 2021 03:48:14 +1000 (AEST) Received: from minnie.tuhs.org (localhost [127.0.0.1]) by minnie.tuhs.org (Postfix) with ESMTP id 1ADFB9C870; Sat, 4 Sep 2021 03:48:01 +1000 (AEST) Authentication-Results: minnie.tuhs.org; dkim=pass (2048-bit key; secure) header.d=jfloren.net header.i=@jfloren.net header.b="o38AudSy"; dkim-atps=neutral Received: by minnie.tuhs.org (Postfix, from userid 112) id 42DD79C870; Sat, 4 Sep 2021 03:47:59 +1000 (AEST) X-Greylist: delayed 318 seconds by postgrey-1.36 at minnie.tuhs.org; Sat, 04 Sep 2021 03:47:55 AEST Received: from mail-4327.protonmail.ch (mail-4327.protonmail.ch [185.70.43.27]) by minnie.tuhs.org (Postfix) with ESMTPS id 60D1A9BA1E for ; Sat, 4 Sep 2021 03:47:55 +1000 (AEST) Received: from mail-0301.mail-europe.com (mail-0301.mail-europe.com [188.165.51.139]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) by mail-4321.protonmail.ch (Postfix) with ESMTPS id 4H1Q9X4zW4z4x4s6 for ; Fri, 3 Sep 2021 17:42:40 +0000 (UTC) Authentication-Results: mail-4321.protonmail.ch; dkim=pass (2048-bit key) header.d=jfloren.net header.i=@jfloren.net header.b="o38AudSy" Date: Fri, 03 Sep 2021 17:42:33 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=jfloren.net; s=protonmail; t=1630690954; bh=4wXa9t8oaTTHKerJT3250CSLdL0phm1R5G5zTr4/++g=; h=Date:To:From:Reply-To:Subject:In-Reply-To:References:From; b=o38AudSy6dHNjcvysR5kLrBd4/s/bXAUOk6+bxUto6ppbKj5Xk98c5gLYluiUnIhc U4V7x6YFRWOx/jLy/L1WOnqgRdjRffog7gSTIxT8obun2jXNGbhmbOP7H+dQOPwZw3 j3aectjbMmvQto/8fLxS82nvYly0T5YkL2al5JZ+KYp6woLjMuVj1I8thUx1Scaw2L xU/5m4xd4k+D9AM1AbTN5hGvChMh7DE7UgBm6KTKjDr42UnjrXHgVGG73tsrSmb1VD PT0oGMlKKlpF0higLtyhEDbNMglJkJdRGehwTT2flZHSBz1hy0aVJ9s5z/xoubx6Zs VAfmcN2h1ovBQ== To: The Eunuchs Hysterical Society From: John Floren Message-ID: In-Reply-To: <20210903172848.GF13471@mcvoy.com> References: <20210903172848.GF13471@mcvoy.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [TUHS] ATC/OSDI'21 joint keynote: It's Time for Operating Systems to Rediscover Hardware (Timothy Roscoe) X-BeenThere: tuhs@minnie.tuhs.org X-Mailman-Version: 2.1.26 Precedence: list List-Id: The Unix Heritage Society mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: John Floren Errors-To: tuhs-bounces@minnie.tuhs.org Sender: "TUHS" When I took Computer Architecture, "reasoning" about out-of-order execution= involved 30-page worksheets where we could track the state of the Tomasulo= algorithm through each iteration. It was ludicrously slow work, and wouldn= 't be a lot of fun even if you had a computerized tool to help step through= things instead. If you're talking about a modern Intel CPU where your compiler emits CISC i= nstructions which are actually implemented in RISC instructions in the micr= ocode, which in turn get rewritten and reordered internally by the CPU... i= t's hard to fault programmers for thinking at the level of the instruction = set that's presented to them, even if it looks like a PDP-11. The above should not be read as an endorsement of the CPU status quo, of co= urse :) john =E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90 Original Me= ssage =E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90 On Friday, September 3rd, 2021 at 10:28 AM, Larry McVoy wrot= e: > I am exactly as Adam described, still thinking like it is a PDP-11. > > Such an understandable machine. For me, out of order execution kind > > of blew up my brain, that's when I stopped doing serious kernel work, > > I just couldn't get to a mental model of how you reasoned about that. > > Though I was talking to someone about it, maybe Clem, recently and > > came to the conclusion that it is fine, we already sort of had this > > mess with pipelines. So maybe it is fine, but out of order bugs my > > brain. > > On Fri, Sep 03, 2021 at 10:10:57AM -0700, Adam Thornton wrote: > > > Much of the problem, I think, is that: > > > > 1. an idealized PDP-11 (I absolutely take Warner's point that that > > > > idealization never really existed) is a sufficiently simple model t= hat a > > > > Bear Of Little Brain, such as myself, can reason about what's going= to > > > > happen in response to a particular sequence of instructions, and ge= t fairly > > > > proficient in instructing the machine to do so in a non-geological > > > > timeframe. > > > > 2. a modern CPU? Let alone SoC? Fuggedaboutit unless you're way, way > > > > smarter than I am. (I mean, I do realize that this particular venue= has a > > > > lot of those people in it...but, really, those are people with > > > > extraordinary minds.) > > > > > > There are enough people in the world capable of doing 1 and not 2 that = we > > > > can write software that usually mostly kinda works and often gets stuff > > > > done before collapsing in a puddle of nasty-smelling goo. There aren't > > > > many people at all capable of 2, and as the complexity of systems > > > > increases, that number shrinks. > > > > In short, this ends up being the same argument that comes around every = so > > > > often, "why are you people still pretending that the computer is a PDP-= 11 > > > > when it clearly isn't?" Because, as with the keys and the streetlight, > > > > that's what we have available to us. Only a grossly oversimplified mode= l > > > > fits into our heads. > > > > Adam > > > > On Fri, Sep 3, 2021 at 8:57 AM Warner Losh imp@bsdimp.com wrote: > > > > > On Wed, Sep 1, 2021 at 4:00 PM Dan Cross crossd@gmail.com wrote: > > > > > > > I'm curious about other peoples' thoughts on the talk and the overa= ll > > > > > > > > topic? > > > > > > My comment is that the mental map that he presents has always been a = lie. > > > > > > At least it's been a lie from a very early time. > > > > > > Even in Unibus/Qbus days, the add-in cards had some kind of processor > > > > > > on it from an early time. Several of the VAX boards had 68000 or simi= lar > > > > > > CPUs that managed memory. Even the simpler MFM boards had buffer > > > > > > memory that needed to be managed before the DMA/PIO pulled it out > > > > > > of the card. There's always been an element of different address spac= es > > > > > > with different degrees of visibility into those address spaces. > > > > > > What has changed is all of these things are now on the SoC die so > > > > > > you have good visibility (well, as good as the docs) into these thing= s. > > > > > > The number of different things has increased, and the for cross domai= n > > > > > > knowledge has increased. > > > > > > The simplistic world view was even inaccurate at the start.... > > > > > > Warner > > Larry McVoy lm at mcvoy.com http://www.mcvoy.com/lm