From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pz0-f48.google.com (mail-pz0-f48.google.com [209.85.210.48]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 999B22012AC for ; Sat, 5 May 2012 15:48:08 -0700 (PDT) Received: by dadz8 with SMTP id z8so1797652dad.7 for ; Sat, 05 May 2012 15:48:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; bh=BgYWuZfAhwlVc+B5u5rU1bUQkke16uKq+Cmes8Oi95E=; b=cNSWeiTSeT1lwONsrtb7Pgck4rKXRVeaRH1aSbIRJMhpSYMLzvg6H0SoQy67E/1pG5 EOrG/SbFpIByl3JkNQ7f+sL+q2u4sacHMXZQBAawQ/HtmhScOFevhx7/FO1zjJTcna3S htjosuvA/OXq1OeravJKN4rtpzieMp8yKmL2Uq2HELxO1AMe/dvYhNUuqHCAxDj51JwA h2wGYFuXW/CUrJHBnVaI0TrVEWhfl+BXuMS3Jr0RRB57vRiusPOCnGEooQiPrmmyVFKr 7uze60Jla1ydSiduUOajWRK/jhJ4DQUFZLDSMPlhNtymxoYrw+44tRn0JrtmLrPz/lp2 1HVg== Received: by 10.68.228.106 with SMTP id sh10mr9466178pbc.107.1336258088150; Sat, 05 May 2012 15:48:08 -0700 (PDT) Received: from ?IPv6:2001:4f8:3:203::c001? ([2001:4f8:3:203::c001]) by mx.google.com with ESMTPS id h10sm13014617pbh.69.2012.05.05.15.48.06 (version=SSLv3 cipher=OTHER); Sat, 05 May 2012 15:48:06 -0700 (PDT) Message-ID: <4FA5AE25.1080506@gmail.com> Date: Sat, 05 May 2012 15:48:05 -0700 From: dave taht User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120410 Thunderbird/11.0.1 MIME-Version: 1.0 To: Eric Dumazet References: <1336217671-20384-1-git-send-email-dave.taht@bufferbloat.net> <1336218794.3752.508.camel@edumazet-glaptop> <1336229343.3752.516.camel@edumazet-glaptop> <1336249251.3752.558.camel@edumazet-glaptop> <1336250168.3752.560.camel@edumazet-glaptop> <1336252281.3752.561.camel@edumazet-glaptop> <4FA597C0.7090206@gmail.com> <1336252832.3752.563.camel@edumazet-glaptop> <4FA5A3B8.7020808@gmail.com> <1336255783.3752.573.camel@edumazet-glaptop> <4FA5AB05.9030305@gmail.com> <1336257554.3752.578.camel@edumazet-glaptop> In-Reply-To: <1336257554.3752.578.camel@edumazet-glaptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: codel@lists.bufferbloat.net, =?UTF-8?B?RGF2ZSBUw6RodA==?= Subject: Re: [Codel] [PATCH v5] pkt_sched: codel: Controlled Delay AQM X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 05 May 2012 22:48:10 -0000 On 05/05/2012 03:39 PM, Eric Dumazet wrote: > On Sat, 2012-05-05 at 15:34 -0700, dave taht wrote: >> On 05/05/2012 03:09 PM, Eric Dumazet wrote: >>> On Sat, 2012-05-05 at 15:03 -0700, dave taht wrote: >>> >>>> Maybe on your arch, but highly doubtful on a 680Mhz mips that isn't even >>>> superscalar. >>>> >>> CPU are fast, memory is slow. >>> >>>> I'd prefer to leave it in and be able to compile it out, and actually >>>> measure the difference. >>> You optimize the case where there is no need to optimize (small queue) >>> >>> I can see count bigger than 100000 with 20 concurrent netperf >>> >>> This makes no sense to have a cache so big. >>> >>> Or there is a bug in codel >> The original reciprocol approximation test code rapidly goes AWOL after >> exceeding 2^8. >> >> I went looking for butterflies and didn't see any in the scaled code in >> the range 0-100000, >> and they would only take flight briefly, so... >> >> However I have not corrected it for BITS_PER_LONG as per our 4AM >> discussion. > You should use the exact code in kernel. (using BITS_PER_LONG) > >> ... >> >> interval/sqrt(99999)=316229 approx :6250190 19.76475908 interval/scaled: >> 316236 1.00002214 >> >>> > If you read the code , there is no possible overflow, even with very > large 'u32 count' > > anyway the problem is q->count keeps increasing under load. > > Only when load is stopped for a while, count is reset to 1 > Stalking butterflies. ( http://en.wikipedia.org/wiki/File:Lorenz_attractor_yb.svg ) I suspected also we would have issues as we hit some natural quantums (clock rate/interrupt rate/bql estimator etc) but for all I know it's just a plain bug. I need a reboot. Goin to dinner. > > > > >