From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qg0-x231.google.com (mail-qg0-x231.google.com [IPv6:2607:f8b0:400d:c04::231]) (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 B00A821F6CF for ; Sun, 1 Nov 2015 16:20:53 -0800 (PST) Received: by qgeo38 with SMTP id o38so105526897qge.0 for ; Sun, 01 Nov 2015 16:20:52 -0800 (PST) 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=t7GldCCGV01HDNZ5/gYGxOeEKuZix6XK66Q95fwou2s=; b=J7WYpxmv93jbqtZCpH4HzdaOSwMVFdW2MDYtLzAfsPKAL34dRdxBp2ieE3zS/SCO+X 8HnuN/ybXOZLwplmqG7ZlAGtm7P4k5a7WUDKKebguypAlI2ychc9xaTYIieA55tMWN8/ EQy2izQFuVGpZ2+r7lcHfRB6KL0OFzpjY914M6/HZZB0/xK5o3uhDbqZHTtE66OaMNHX LxAoRlJjc4n5lC9r66qol3nFFE9VqKksef49HpIYZjIkUcTk0ZaukNWJkUfPMdbMUHU/ g8CbdC+vki6IwdBWwI8uB2lrbVo8LUKVw9YctXQWGY/WbSHyZoMyxjGkIvHvFkqlQ+ZC tX5g== MIME-Version: 1.0 X-Received: by 10.140.20.213 with SMTP id 79mr26309418qgj.39.1446423652034; Sun, 01 Nov 2015 16:20:52 -0800 (PST) Received: by 10.140.85.39 with HTTP; Sun, 1 Nov 2015 16:20:51 -0800 (PST) In-Reply-To: References: Date: Mon, 2 Nov 2015 00:20:51 +0000 Message-ID: From: Alan Jenkins To: Kevin Darbyshire-Bryant Content-Type: text/plain; charset=UTF-8 Cc: "cake@lists.bufferbloat.net" Subject: Re: [Cake] cake target corner cases? X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 Nov 2015 00:21:16 -0000 On 01/11/2015, Kevin Darbyshire-Bryant wrote: > > Can't give full explanation now but the bytes per ns calculation which is > used as a basis for target on 'slow' links uses mtu*1.5 > > -- > Cheers, Right. And mtu*1.5 matches better than my math, if I look at Sebs figures again. Oops :). I thought SQM works fine with mtu * 1.0. But cake has been like this since at least April, and I didn't notice an extra 7ms when I tried it. Confusing. Sebs 12.5% is indeed 1/8th. (See last line). u32 byte_target = mtu + (mtu >> 1); /* MTU * 1.5 */ ... byte_target_ns = (byte_target * rate_ns) >> rate_shft; b->cparams.target = max(byte_target_ns, ns_target); b->cparams.interval = max(rtt_est_ns + b->cparams.target - ns_target, b->cparams.target * 8); Maybe this keeps the target/interval ratio from going too far over the recommended 10%. Though that's not what CoDel says to do. In the CoDel draft you just don't drop below 1 MTU. You don't adjust target for the rate. There's no suggestion to increase interval either. It makes sense that long transmission times add to the expected rtt (SQM does this too). I can't see what the justification is for `target * 8` though. If there's a good reason maybe it could use a comment. Thanks Alan