From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-x231.google.com (mail-qk0-x231.google.com [IPv6:2607:f8b0:400d:c09::231]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 073CA3BA8E for ; Wed, 30 May 2018 14:54:28 -0400 (EDT) Received: by mail-qk0-x231.google.com with SMTP id d125-v6so15195148qkb.8 for ; Wed, 30 May 2018 11:54:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=DbTSirj05mLqL2T3UFB8LUu46LaS5XcD3X06AOL+JEs=; b=pPbHqAlyBYe58flAEEXI8Z2Zo0OxS5Br7OLJJeyL07lfP1xUCi6S0b5riEbodi4G7+ VHCQqrdRDNesvVsfrGbd+IFCsBbnsPZ+OYyJ1G6ofUNyDGvRSS33kZowGUEwbN0icFNZ ZnbrquTaFX/b+0jTx4AOD2g5P8D/lkWdkAbg3VRsKQMIVS6vm7Aq4gtjvKK68CNdP2il rmJIJuSvb4bgXCOrVJXAKtJGbhSxq2iEZYk0ftKNNhInM52Za0VtdCD10gSHd0qiMgBe BDrYnb8MZJme7Xb/viwM09t3iq6KRVMrjMPPPneFjyrCAmPM6XVP2oDUR5hrYwoQNEHF L8SA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=DbTSirj05mLqL2T3UFB8LUu46LaS5XcD3X06AOL+JEs=; b=VmBU8EFEy7hHCcPiObkp63V8T9GQJUSxt9mJy78ZA0VYv6+74xzUodfrB3y25Uwxon x3841FVMnXDYeCyZpRgdyoebec45VfRXFDSwExCJG0NbIBhE5rTju1dIlA2TcElMS/zM NKXflKh1FdfHkzQUWVRPOdJAmMo/jIhkh9vuAyIcCWNVgACgI5JjCsagyfhc3UuWLQDM u8pbGEOFd8T7cwIaZC46EQan8/yPLDV46IS6uVRsQFnAsKRx9v2mH3JMQO4WWeNyuM+T 6wRmGFuO/dZHvabG5Nn4iPGL2dviWLIkAKYoTgd8ejJL2P86/69xB+YPpYdHDZv5Opiw p97Q== X-Gm-Message-State: APt69E00C/tUTCtr8WQaCuwpvRcX2+UaSdLSMZxW98dCj9FhWVJ7Qmz9 dSINUI2r47FrCyrne3ZcqzoblhtIgwdbFcMfxmk= X-Google-Smtp-Source: ADUXVKK20XSEWVdAIOz0I1qHyFtSThM0DBdOIu8alogW868qfhSkTpaWwi4lBcnGMTLQ7g+1Xfu5bkcAkdjlMnVQkfk= X-Received: by 2002:a37:646:: with SMTP id 67-v6mr3464972qkg.35.1527706467408; Wed, 30 May 2018 11:54:27 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:ac8:7193:0:0:0:0:0 with HTTP; Wed, 30 May 2018 11:54:26 -0700 (PDT) In-Reply-To: References: From: Dave Taht Date: Wed, 30 May 2018 11:54:26 -0700 Message-ID: To: Bob McMahon Cc: Make-Wifi-fast Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [Make-wifi-fast] emulating wifi better - coupling qdiscs in netem? X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 30 May 2018 18:54:28 -0000 On Wed, May 30, 2018 at 11:32 AM, Bob McMahon wr= ote: > Sorry, I may be coming late to this. What exactly is the goal? Instead = of > emulating interference with netem is it possible to create real > interference? Interference to me is a secondary, but important part of the problem. The core requirement is somehow emulating the single transmitter at a time behavior of wireless technologies. In this way of thinking, an interfere-er is just another transmitter in emulation. Linux's behaviors are all full duplex, except at the very lowest driver levels. Being able to move the concept of a "single bulk transmitter at a time" much higher in stack (at least, for netem emulation), is what I'd like to do. Being better able to reliable look at the behaviors of e2e protocols with a decently correct wireless emulation... Does that help? Just getting to where I could describe the problem(s) well enough to talk about 'em in the mailing list has taken me forever, and if I/we can get to where we can describe the problem better, maybe solutions will materialize. ;) Did anyone but me ever play with the slotting models I put into netem last = year? > > Bob > > On Wed, May 30, 2018 at 10:28 AM, Dave Taht wrote: >> >> The match to reality of my "wifi slotting" code for netem was so >> disappointing that I was extremely reluctant to push support for it up >> to mainline iproute2. >> >> I've now spent months failing to come up with something that >> could emulate in linux the non-duplex behavior and arbitration steps >> that wifi goes through in order to find a new station to transmit to, >> or receive from, using netem as a base. >> >> Getting that non-duplex behavior right is the *single most important >> thing*, I think, for trying to emulate real wireless behaviors in >> real time that I can think of (and to thus be able to run and improve >> various e2e transports against it). >> >> A potential tc API seems simple: >> >> tc qdisc add dev veth1 root netem coupled # master (AP) >> tc qdisc add dev veth2 root netem couple veth1 # client >> tc qdisc add dev veth3 root netme couple veth2 # client >> >> Something more complicated would be to create some sort of >> arbitration device and attach that to the qdiscs. (which would make >> it more possible to write arbitration devices to emulate lte, gpon, >> cable, wireless mesh and other non-duplex behaviors in real time) >> >> But how to convince qdiscs to be arbitrated, only allowing one in a >> set to transmit at the same time? (and worse, in the long run, >> allowing MU-MIMO-like behaviors). >> >> I'm tempted to *not* put my failed thinking down here in the hope that >> someone says, out there, "oh, that's easy, just create this structure >> with X API call and use Y function and you're clear of all the >> potential deadlock and RCU issues, and we've been doing that for >> years, you idiot! Here's the code for how we do it, sorry we didn't >> submit it earlier." >> >> What I thought (*and still think*) is of creating a superset of the >> qdisc_watchdog_schedule_ns() function is a start at it: >> >> tag =3D qdisc_watchdog_create_arb("some identifier"); >> qdisc_watchdog_schedule_arb(nsec, tag); /* null tag =3D schedule_ns */ >> >> which doesn't allow that qdisc instance to be run until the arbitrator >> says it can run (essentially overriding the timeout specified) >> >> But I actually wouldn't mind something that worked at the veth, or >> device, rather than qdisc level... >> >> thoughts? >> >> PS I just spent several days working on another aspect of the problem, >> which is replaying delay distributions (caused by interference and >> such)... and that, sigh, to me, also belongs in some sort of >> arbitration device rather than directly in netem. Maybe tossing netem >> entirely is the answer. I don't know. >> >> -- >> >> Dave T=C3=A4ht >> CEO, TekLibre, LLC >> http://www.teklibre.com >> Tel: 1-669-226-2619 >> _______________________________________________ >> Make-wifi-fast mailing list >> Make-wifi-fast@lists.bufferbloat.net >> https://lists.bufferbloat.net/listinfo/make-wifi-fast > > --=20 Dave T=C3=A4ht CEO, TekLibre, LLC http://www.teklibre.com Tel: 1-669-226-2619