From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-x233.google.com (mail-lf0-x233.google.com [IPv6:2a00:1450:4010:c07::233]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 667343B260 for ; Tue, 27 Sep 2016 23:49:54 -0400 (EDT) Received: by mail-lf0-x233.google.com with SMTP id y6so39302909lff.1 for ; Tue, 27 Sep 2016 20:49:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=SrbHxxIxfNIrD1yGR8kYVGWjICKMENTD0xtobTHmTO4=; b=vDPRiX4U+Lq+AeUxp1wOdTCUz2a0tT3vEUThkjpOph167xSaSVtI/BMNChMsBqjwKK mcInpjGazcjuv08NKOyygn3qUWQgm9DgWOXoOyGyUONQ1YxPRorTUgWHf5OeGxj36+r+ Lb49smfCbzBQSYr+mRSL2SflA8sereLzHAZ9O6T971ZpRHqbzD3u5B+RWt730BqztSV8 Z81/NSq9DmA1TP4zQ0AjMEwV3gXTBr83yJyKHEbVeTqbVnqEnY9VBgtBrTGCakLaQ8d0 wV3zsQXcAedSQuLJhBRhU5O/Y48bWMJJ8eKiOO9mTHael2bg27K0VQ249hiZgXFd4UjQ j5Hg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=SrbHxxIxfNIrD1yGR8kYVGWjICKMENTD0xtobTHmTO4=; b=gQW3AT6RzBd/f+FzfiPF9jWXUZ5/L2fVtlNuZ1zgrnQuQ/ONvHGALQ9s5IHyPA1JcS 9uAIvZwhueVx4FYMkBlOQq0pNkcP3sm0nfxS3SPzDtSAIr87V/UrVTpgdFTBhCbKhJHh cmbIr1zwIl/wfLwCFmKhAWlx7L+EInIsBMaPOKiM4VqOMB+f9JJdqpg339b6vmjX/lfD xUVORZ723wvrsJMH8FIRA2xcNFI1NvAGKP9e3cjl5H4y8mxjjTSxLLbP426WUSb1Nn5m g8uxkPscCXeKfu4kBrBmVZsxWAREscj7IQoMO4fXzVdyp12gUzliGdg6y2bl+WDOTVQU HIqA== X-Gm-Message-State: AE9vXwMQN8rFB9xm5y+KbBwxdNCTmfAl8cv6fGQAPr9NB0wmfQuH+ED2uqGKiG0S90Gaog== X-Received: by 10.25.89.70 with SMTP id n67mr12066665lfb.163.1475034592692; Tue, 27 Sep 2016 20:49:52 -0700 (PDT) Received: from [192.168.100.13] (37-33-90-35.bb.dnainternet.fi. [37.33.90.35]) by smtp.gmail.com with ESMTPSA id g88sm231344ljg.25.2016.09.27.20.49.51 (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 27 Sep 2016 20:49:52 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) From: Jonathan Morton In-Reply-To: Date: Wed, 28 Sep 2016 06:49:50 +0300 Cc: cake@lists.bufferbloat.net Content-Transfer-Encoding: quoted-printable Message-Id: <55B501FC-5370-44DA-93EC-37EBF20AB747@gmail.com> References: <3a99770e-6350-471f-72b6-b209d7d77d75@darbyshire-bryant.me.uk> <8425FD26-5C1F-42B5-9087-01D81E1ED7F5@gmail.com> <3c28ec73-36e7-dfed-fad8-1a694d4ceeca@darbyshire-bryant.me.uk> <8555AC94-885C-41C1-BE12-40C3C3E96810@gmail.com> To: Kevin Darbyshire-Bryant X-Mailer: Apple Mail (2.3124) Subject: Re: [Cake] de-natting & host fairness X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 28 Sep 2016 03:49:54 -0000 > On 28 Sep, 2016, at 06:33, Kevin Darbyshire-Bryant = wrote: >=20 > those ternaries are if/else in disguise... Many CPUs can handle those as conditional moves without branching - = including ARM in particular; near-universal conditional execution was = one of its original headline features. Most x86 CPUs (except very old = ones) and some of the embedded-class PowerPCs (which are often found in = =E2=80=9Cbig=E2=80=9D network appliances) also qualify. Unswitching = those would potentially be a retrograde step on those CPUs. However the presence of a conditional function call suggests that = unswitching would not in fact be harmful, except for some duplication of = source code - since the branch has to be made anyway. I think many = compilers would be able to perform the loads before the branch and the = stores after it, which would execute very slickly, while some CPUs do = not execute large numbers of conditional moves very efficiently. - Jonathan Morton