From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-03-ewr.dyndns.com (mxout-082-ewr.mailhop.org [216.146.33.82]) by lists.bufferbloat.net (Postfix) with ESMTP id C1C472E0079 for ; Mon, 28 Feb 2011 16:55:38 -0800 (PST) Received: from scan-02-ewr.mailhop.org (scan-02-ewr.local [10.0.141.224]) by mail-03-ewr.dyndns.com (Postfix) with ESMTP id 22AA7788DB8 for ; Tue, 1 Mar 2011 00:55:02 +0000 (UTC) X-Spam-Score: 0.0 () X-Mail-Handler: MailHop by DynDNS X-Originating-IP: 74.125.82.171 Received: from mail-wy0-f171.google.com (mail-wy0-f171.google.com [74.125.82.171]) by mail-03-ewr.dyndns.com (Postfix) with ESMTP id 51327788D91 for ; Tue, 1 Mar 2011 00:55:01 +0000 (UTC) Received: by wyf22 with SMTP id 22so5234605wyf.16 for ; Mon, 28 Feb 2011 16:55:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:content-type :content-transfer-encoding; bh=uvjjKqRAkhmQuvTFXLQWjfO/sDGQshEZFW04fGXuToI=; b=UN3iVKQc9s1/zM6tC9lyc/SNYDA6YHkOlOrlVFjZPuXSq8WSv6MurJxYc6GqNRtr20 TEkgWzuYANe6PRP/0lji2+QsGU6nN6EIMqMaILYoNwv+jxuSOpkH7BEw6FbH8yeHsCBE FRaKrmNibzBTB5m9DwYfR2kfhub9GpGz4UjJE= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:content-type :content-transfer-encoding; b=vhJzjaHQM7dDMtuxTqUPKxrx/G9EpPyWPqcdGu3nh4j4iNodxS2cR2x02LIyLZgpT/ QKJwmjMV/fyUK0TJo2JAEs79kq64/ExOdp/N/P3FS3uTWzjjIJwxM6L++RvSV/6ZpZaY 5qzJC8n7297lopwrOGLfE3wo0ANb6/gputA+0= MIME-Version: 1.0 Received: by 10.216.163.11 with SMTP id z11mr5411225wek.36.1298940900607; Mon, 28 Feb 2011 16:55:00 -0800 (PST) Sender: devinlindsay@gmail.com Received: by 10.216.8.137 with HTTP; Mon, 28 Feb 2011 16:55:00 -0800 (PST) In-Reply-To: <87wrkkpa89.fsf@cruithne.co.teklibre.org> References: <87wrkkpa89.fsf@cruithne.co.teklibre.org> Date: Mon, 28 Feb 2011 16:55:00 -0800 X-Google-Sender-Auth: Ztky-fxC51JI9ZewP1oc4K60jk8 Message-ID: Subject: Re: latency limiting to 4ms? From: D Lindsay To: bloat-devel@lists.bufferbloat.net Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable X-BeenThere: bloat-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: "Developers working on AQM, device drivers, and networking stacks" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 01 Mar 2011 00:55:39 -0000 Hi Dave, I started to think of what one who doesn't know much about kernel specifics but has some practical experience (growing an 802.11 WAN over a decade) would say. Here is a bit of real-world information maybe related to buffer-bloat and buffers. It may be interesting as my connection (unique* rural broadband** - see below) is from a MacBook Pro via an Airport to several different "hosts" which I've abbreviated in caps: LM - the local MacBook that I am testing from AP - the airport, configured a/n and operating in 802.11n mode on 5.8GHz RM - a mac mini connected to the GB ethernet side of the airport VM1 - A virtual ubuntu machine running in Oracle's Virtual Box on RM VM2 - A virtual debian machine running in VMware Fusion on RM GW - my internet gateway (a 900MHz tranzeo client) GG - one of google's machines AV - an ubuntu amazon cloud tiny instance in Virginia An additional note is that the AP ethernet (Gb) is connected to the GW via a 10/100 switch and from the GW is s 900MHz hop about 300m through scrub to a radio which links at 2.4GHz to a radio about 4km away and then via a 3.5MHz link, another 4km to a length of fibre=85 not sure about the exact details, but the E10 on the fibre runs about 60km and then goes about 100km via microwave which is not actually a straight line, *but an L-shaped link that actually bounces off a passive reflector (looks like a billboard) on a convenient mountain peak. My connection is then rate limited by equipment at that point to 1Mbps down/512kbps up (not quit IC definition of broadband) and it then continues on fibre to an "outdated switch" and from there via fibre to on of the internet exchanges and off to google. (I could have a bit wrong, but should let you know the connection is a bit unique). **Final note -- when the E10 "saturates" surfing is painful, utube can't be watched in realtime, and voip gets pretty unusable - thankfully people stop using it and it gets better :D Here are the relevant kernels: ~~~~~~~~~~~~~~~~~~~~~~~ LM~ uname -a (10.0.1.4) Darwin LM-MacBook-Pro.local 10.4.1 Darwin Kernel Version 10.4.1: Fri Jul 16 23:04:20 PDT 2010; root:xnu-1504.7.51~1/RELEASE_I386 i386 RM~ uname -a (10.0.1.3) Darwin RM-mac-mini.local 9.8.0 Darwin Kernel Version 9.8.0: Wed Jul 15 16:55:01 PDT 2009; root:xnu-1228.15.4~1/RELEASE_I386 i386 VM1~ ssh -l root 10.0.1.5 uname -a Linux vm1 2.6.35-22-generic #33-Ubuntu SMP Sun Sep 19 20:34:50 UTC 2010 i686 GNU/Linux VM2~ ssh -l root 10.0.1.27 uname -a Linux vm2 2.6.26-2-686 #1 SMP Mon Jun 21 05:58:44 UTC 2010 i686 GNU/Linux AV ~ uname -a Linux AV 1 2.6.35-24-virtual #42-Ubuntu SMP Thu Dec 2 05:01:52 UTC 2010 i686 GNU/Linux Here are some latencies. The method I used to saturate the link was to scp two files at the same time in each direction between LM and VM1. Aggregate average throughput for the scp transfers was 9.8MBps. Baseline latencies: (802.11n unloaded) ------------------------------------------ LM ~ --- 10.0.1.4 ping statistics --- 28 packets transmitted, 28 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 0.047/0.104/0.133/0.023 ms AP ~ --- 10.0.1.1 ping statistics --- 12 packets transmitted, 12 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 0.941/2.791/3.087/0.560 ms RM ~ --- 10.0.1.3 ping statistics --- 20 packets transmitted, 20 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 3.447/3.759/5.691/0.488 ms VM1 ~ --- 10.0.1.5 ping statistics --- 16 packets transmitted, 16 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 3.076/3.582/5.622/0.578 ms VM2 ~ --- 10.0.1.27 ping statistics --- 14 packets transmitted, 14 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 1.281/3.426/5.513/0.981 ms GW ~ --- 192.168.100.1 ping statistics --- 8 packets transmitted, 8 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 3.215/3.444/3.747/0.186 ms GG ~ --- www.l.google.com ping statistics --- 6 packets transmitted, 6 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 45.662/50.934/54.759/2.748 ms AV --- 50.70.250.xx ping statistics --- 9 packets transmitted, 9 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 107.358/116.404/133.579/7.394 ms Latencies Under Load (802.11n loaded by bi-directional scp): =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D LM ~ --- 10.0.1.4 ping statistics --- 33 packets transmitted, 33 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 0.025/0.081/0.153/0.041 ms AP ~ --- 10.0.1.1 ping statistics --- 27 packets transmitted, 27 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 0.797/14.706/36.340/13.125 ms RM ~ --- 10.0.1.3 ping statistics --- 59 packets transmitted, 59 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 1.698/20.292/51.019/13.059 ms VM1 ~ --- 10.0.1.5 ping statistics --- 23 packets transmitted, 23 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 3.237/11.516/27.664/6.489 ms VM2 ~ --- 10.0.1.27 ping statistics --- 24 packets transmitted, 24 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 3.316/16.195/32.407/7.777 ms GW ~ --- 192.168.100.1 ping statistics --- 28 packets transmitted, 28 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 1.299/22.965/51.203/13.779 ms GG ~ --- www.l.google.com ping statistics --- 19 packets transmitted, 19 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 55.531/73.927/91.541/10.198 ms AV~ --- 50.70.250.xx ping statistics --- 16 packets transmitted, 16 packets received, 0.0% packet loss round-trip min/avg/max/stddev =3D 117.986/138.770/169.439/13.535 ms Maybe this is helpful to someone? Devin On Mon, Feb 28, 2011 at 5:19 AM, Dave T=E4ht wrote: > > I'm about to get on a plane but I saw this thread on lkml go by: > > http://groups.google.com/group/linux.kernel/browse_thread/thread/b0add150= 2aafa46f/28dd3798b3d5e4f9?lnk=3Draot > > Where the proposed sched_fifo_ewma.c code in that thread: > > "Well, with 10ms buffer timeout latency goes to 10-20ms on 54Mbit wifi > link (zd1211rw driver) from >500ms (ping rtt when iperf running same > time). So for that it's good enough. " > > And, well, I'd like to go for 4ms across the entire transmit > range. 10-20ms is *just barely* on the wrong side for voip and audio > applications, and the above stat is being measured at 54Mbit. > > Someone care to leap in over there? > > > -- > Dave Taht > http://nex-6.taht.net > _______________________________________________ > Bloat-devel mailing list > Bloat-devel@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/bloat-devel >