From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-x236.google.com (mail-ig0-x236.google.com [IPv6:2607:f8b0:4001:c05::236]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id E881821F2D2; Mon, 1 Sep 2014 13:25:09 -0700 (PDT) Received: by mail-ig0-f182.google.com with SMTP id a13so6218211igq.9 for ; Mon, 01 Sep 2014 13:25:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=rVqcaSpeb+jhDBXkrIN6BK0/9We0d4PErHNEYy6ObBQ=; b=V8BvtzuUo9NJp5ts+IESgzjDV7tRW8QYrvjlUjLM5pckn1P3Zqje8repMx/C1yrC4N rfKw8vpi5xBcjSJpN2CesTM0LD1Mg2HRyCzSucqw20wYAx+GwTWRgZzCFi1iQvAvHvXQ bXNgeIIKeVA3fXIOsX6G9gSQfR4DwHR5HQ9o1LI92wrggJeJzgBW0jSLiWRvhz5qDqwP HeqTZQ/+Obw1HsuB3UlxW9EMyFkC0XSl9MW/1d4mhYyK3D/g/J2dAiWgOpmdHb7F5n0y yvcB0X6h/6DEWRNQ4KanAZehQaSgUJs80lTmViqB6QkJuc8pqErBs075vehi7fQI476o cHJA== MIME-Version: 1.0 X-Received: by 10.50.111.132 with SMTP id ii4mr23787899igb.8.1409603108950; Mon, 01 Sep 2014 13:25:08 -0700 (PDT) Received: by 10.64.243.196 with HTTP; Mon, 1 Sep 2014 13:25:08 -0700 (PDT) In-Reply-To: References: <87ppfijfjc.fsf@toke.dk> <4FF4917C-1B6D-4D5F-81B6-5FC177F12BFC@gmail.com> <4DA71387-6720-4A2F-B462-2E1295604C21@gmail.com> <0DB9E121-7073-4DE9-B7E2-73A41BCBA1D1@gmail.com> Date: Mon, 1 Sep 2014 13:25:08 -0700 Message-ID: From: Aaron Wood To: Dave Taht Content-Type: multipart/alternative; boundary=047d7b414110955965050206cc5b Cc: Jonathan Morton , "cerowrt-devel@lists.bufferbloat.net" , bloat Subject: Re: [Cerowrt-devel] [Bloat] Comcast upped service levels -> WNDR3800 can't cope... X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 01 Sep 2014 20:25:10 -0000 --047d7b414110955965050206cc5b Content-Type: text/plain; charset=UTF-8 > > But this doesn't really answer the question of why the WNDR has so much > lower a ceiling with shaping than without. The G4 is powerful enough that > the overhead of shaping simply disappears next to the overhead of shoving > data around. Even when I turn up the shaping knob to a value quite close > to the hardware's unshaped capabilities (eg. 400Mbps one-way), most of the > shapers stick to the requested limit like glue, and even the worst offender > is within 10%. I estimate that it's using only about 500 clocks per packet > *unless* it saturates the PCI bus. > > > > It's possible, however, that we're not really looking at a CPU > limitation, but a timer problem. The PowerBook is a "proper" desktop > computer with hardware to match (modulo its age). If all the shapers now > depend on the high-resolution timer, how high-resolution is the WNDR's > timer? > > Both good questions worth further exploration. Doing some napkin math and some spec reading, I think that the memory bus is a likely factory. The G4 had a fairly impressive memory bus for the day (64-bit?). The WNDR3800 appears to be used in an x16 configuration (based on the numbers on the memory parts). It may have *just* enough bw to push concurrent 3x3 802.11n through the software bridge interface, which short-circuits a lot of processing (IIRC). The typical way I've seen a home router being benchmarked for the "marketing numbers" is to flow tcp data to/from a wifi client to a wired client. Single socket is used, for a uni-directional stream of data. So long as they can hit peak rates (peak MCS), it will get marked as good for "up to 900Mbps!!" or whatever they want to say. The small cache of the AR7161 vs. the G4 is another issue (32KB vs. 2MB) the various buffers for fq_codel and htb may stay in L2 on the G4, but there simply isn't room in the AR7161 for that, which puts further pressure on the bus. -Aaron --047d7b414110955965050206cc5b Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

=
> But this doesn't really answer the question of why the WNDR has so= much lower a ceiling with shaping than without.=C2=A0 The G4 is powerful e= nough that the overhead of shaping simply disappears next to the overhead o= f shoving data around.=C2=A0 Even when I turn up the shaping knob to a valu= e quite close to the hardware's unshaped capabilities (eg. 400Mbps one-= way), most of the shapers stick to the requested limit like glue, and even = the worst offender is within 10%.=C2=A0 I estimate that it's using only= about 500 clocks per packet *unless* it saturates the PCI bus.
>
> It's possible, however, that we're not really looking at a CPU= limitation, but a timer problem.=C2=A0 The PowerBook is a "proper&quo= t; desktop computer with hardware to match (modulo its age).=C2=A0 If all t= he shapers now depend on the high-resolution timer, how high-resolution is = the WNDR's timer?

Both good questions worth further exploration.

<= /div>
Doing some napkin math and some spec reading, I think that the me= mory bus is a likely factory. =C2=A0The G4 had a fairly impressive memory b= us for the day (64-bit?). =C2=A0The WNDR3800 appears to be used in an x16 c= onfiguration (based on the numbers on the memory parts). =C2=A0It may have = *just* enough bw to push concurrent 3x3 802.11n through the software bridge= interface, which short-circuits a lot of processing (IIRC). =C2=A0=C2=A0

The typical way I've seen a home router being bench= marked for the "marketing numbers" is to flow tcp data to/from a = wifi client to a wired client. =C2=A0Single socket is used, for a uni-direc= tional stream of data. =C2=A0So long as they can hit peak rates (peak MCS),= it will get marked as good for "up to 900Mbps!!" or whatever the= y want to say.

The small cache of the AR7161 vs. the G4 is another iss= ue (32KB vs. 2MB) the various buffers for fq_codel and htb may stay in L2 o= n the G4, but there simply isn't room in the AR7161 for that, which put= s further pressure on the bus.

-Aaron


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