From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f41.google.com (mail-wg0-f41.google.com [74.125.82.41]) (using TLSv1 with cipher RC4-MD5 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 61C9D2012AC for ; Sat, 5 May 2012 15:39:21 -0700 (PDT) Received: by wgbds1 with SMTP id ds1so2187073wgb.4 for ; Sat, 05 May 2012 15:39:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=subject:from:to:cc:in-reply-to:references:content-type:date :message-id:mime-version:x-mailer:content-transfer-encoding; bh=05Zq5ChyzYNa7rxUKdASHCPJUafdKsl6cYY88NPskZY=; b=K6ipb4LyAy4CyeorbUazDCM0m06dk9opdIlFdG3Gofj/sSK97pQ76cRWzrpZDYPVG4 UM9/4P6ekyBobGrNS7ur14qBiPJMq77OAqDtE9Gsj3xqrfx+Bfu9ysXpqBiaue9nw7ma tVSNhfaoyqlPYBeL5auU6sTyW7ba0lEC8LmHraSvLoiawP65RTXQjryuH+LFA51h/zcn jRTB85dk5qMdMzgx17+x/s+7YyJwxS4rvbIxiP9K++ePI1coWMg0Cm00gu1kLiaNlYz1 Hpwn6Canm6B/ZOZaZeTwVqt/hfQI96faomEYlYtTmPbHx3ro2BaFdcT7+veK5a+J2spt 8J4Q== Received: by 10.180.100.230 with SMTP id fb6mr1105879wib.3.1336257559302; Sat, 05 May 2012 15:39:19 -0700 (PDT) Received: from [172.28.130.107] ([74.125.122.49]) by mx.google.com with ESMTPS id j3sm14255063wiw.1.2012.05.05.15.39.16 (version=SSLv3 cipher=OTHER); Sat, 05 May 2012 15:39:18 -0700 (PDT) From: Eric Dumazet To: dave taht In-Reply-To: <4FA5AB05.9030305@gmail.com> 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> Content-Type: text/plain; charset="UTF-8" Date: Sun, 06 May 2012 00:39:14 +0200 Message-ID: <1336257554.3752.578.camel@edumazet-glaptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Cc: codel@lists.bufferbloat.net, Dave =?ISO-8859-1?Q?T=E4ht?= 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 22:39:21 -0000 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