From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.perfora.net (mout.perfora.net [74.208.4.197]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mout.perfora.net", Issuer "Thawte SSL CA" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 02FB121F35D for ; Fri, 12 Sep 2014 04:03:59 -0700 (PDT) Received: from J4 (c-68-50-226-187.hsd1.md.comcast.net [68.50.226.187]) by mrelay.perfora.net (node=mreueus003) with ESMTP (Nemesis) id 0MUmqY-1XrelV3ILs-00Y7hz; Fri, 12 Sep 2014 13:03:52 +0200 From: "Jerry Jongerius" To: "'Eric Dumazet'" References: <000001cfc609$697feb30$3c7fc190$@duckware.com> <1410455146.7106.55.camel@edumazet-glaptop2.roam.corp.google.com> In-Reply-To: <1410455146.7106.55.camel@edumazet-glaptop2.roam.corp.google.com> Date: Fri, 12 Sep 2014 07:03:53 -0400 Message-ID: <000101cfce79$3f6e1f60$be4a5e20$@duckware.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 14.0 Thread-Index: AQJonbn6zg3vUSLijkLaYiZZ7UQnswIfO3mvmrq5mfA= Content-Language: en-us X-Provags-ID: V02:K0:QnVX3D9Mi5mO6xUwyo5TEDJJRhheWjbem5xK9I9z5BL h97AXgQa0aNvs/KSEvx1Z7RML8NWjodcIXD1KuadlkFBmja08a 3GsidAjnUFixeQPfxMDGwQ8UhdB4odQV9DJq0BUOL6saf1wQOb lZ9uzEl4cewVEVtnT1ele1BQBFsUmAhKjRJEuSHU3UXf2QaqSt 8mc54erEs9x9BsNA6nrJKYfJET6kmsA88JpTUU74kT3whDJMET wI8SArqiGXxilqaU48Xw3C564cnvBQvXF1sEIPDk8vl91mnlif HVxh6yX/mH1Y5LpBrk7tebZDgFQKRzaHpwEUpMd8FJFSkSxI6m 8SjLsVhmQH1mo82kGGw3jhHH6EvOAfuLmI8OaTONA X-UI-Out-Filterresults: notjunk:1; Cc: bloat@lists.bufferbloat.net Subject: Re: [Bloat] What is wrong with Microsoft's receive window auto-tuning? X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 12 Sep 2014 11:04:28 -0000 I have published some more details here: http://www.duckware.com/blog/microsoft-windows-receive-window-auto-tuning= -causes-bufferbloat/index.html The problem is that a 'receive window set too large' causes (bufferbloat = and) RTT times to increase to over 200ms, which then all of sudden = causes bad things to start happening when there is a lost packet. It almost looks like the algorithm does not account for bufferbloat -- = which means that during bufferbloat, RTT times increase, and the = algorithm computes an even large receive window, which causes even more = bufferbloat. Just curious. There seems to be a lot of room for improvement in the = algorithms... - Jerry -----Original Message----- From: Eric Dumazet [mailto:eric.dumazet@gmail.com]=20 Sent: Thursday, September 11, 2014 1:06 PM To: Jerry Jongerius Cc: bloat@lists.bufferbloat.net Subject: Re: [Bloat] What is wrong with Microsoft's receive window = auto-tuning? On Mon, 2014-09-01 at 13:23 -0400, Jerry Jongerius wrote: > I am noticing (via WireShark traces) at times that Microsoft's=20 > (Windows 7) receive window auto-tuning goes horribly wrong, causing=20 > significant buffer bloat. And at other times, the tuning appears to = work just fine. >=20 > For example, BDP suggests a receive window of 750k, and most often=20 > Windows tunes around 1MB -- but at other times, it will tune to 3.8MB=20 > (way more than it should). >=20 > Is anyone aware of any research either pointing out how their tuning=20 > algorithm works, or of known bugs/problems with the algorithm? How BDP suggests a receive window of 750k ? If BDP _is_ 750k, then 3.8 MB receive window is not insane, it depends = on the amount of drops and how fast you want to recover from drops. 1MB would be to small as a matter of fact.