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From: Jonathan Morton <chromatix99@gmail.com>
To: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
Cc: cake@lists.bufferbloat.net
Subject: Re: [Cake] de-natting & host fairness
Date: Wed, 28 Sep 2016 06:49:50 +0300	[thread overview]
Message-ID: <55B501FC-5370-44DA-93EC-37EBF20AB747@gmail.com> (raw)
In-Reply-To: <d244f790-8ce4-1c02-f43f-03bc20943d07@darbyshire-bryant.me.uk>


> On 28 Sep, 2016, at 06:33, Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk> wrote:
> 
> 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 “big” 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


  reply	other threads:[~2016-09-28  3:49 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-26  3:20 Kevin Darbyshire-Bryant
2016-09-26  3:54 ` Dave Taht
2016-09-26  5:11   ` Dave Taht
2016-09-26  8:54 ` moeller0
2016-09-26 13:02   ` Kevin Darbyshire-Bryant
2016-09-26 13:28     ` moeller0
2016-09-26 14:06       ` Kevin Darbyshire-Bryant
2016-09-26 14:30       ` Jonathan Morton
2016-09-26 15:23         ` moeller0
2016-09-27  1:52 ` Noah Causin
2016-09-27  2:32   ` Kevin Darbyshire-Bryant
2016-09-27  4:20     ` Noah Causin
2016-09-27 14:52     ` Noah Causin
2016-09-27 15:28       ` Kevin Darbyshire-Bryant
2016-09-27 20:40         ` Noah Causin
2016-09-27 20:44           ` Jonathan Morton
     [not found]           ` <CAA93jw6rPE8aAGEiqf7jp3hc1J0ThrVer8PFmFLPBqANdtEixg@mail.gmail.com>
2016-09-27 20:58             ` Noah Causin
2016-09-28  4:38           ` Kevin Darbyshire-Bryant
2016-09-28  5:08             ` Noah Causin
2016-09-27 23:08 ` Jonathan Morton
2016-09-28  2:56   ` Kevin Darbyshire-Bryant
2016-09-28  3:06     ` Jonathan Morton
2016-09-28  3:33       ` Kevin Darbyshire-Bryant
2016-09-28  3:49         ` Jonathan Morton [this message]
2016-09-28  6:07       ` Kevin Darbyshire-Bryant
2016-09-28 11:08         ` Kevin Darbyshire-Bryant
2016-09-28 11:49           ` Dave Taht
2016-09-28 14:11             ` Kevin Darbyshire-Bryant
2016-09-28  5:56   ` Sebastian Moeller

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