From owner-freebsd-hackers Fri Jul 13 11:47:26 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from earth.backplane.com (earth-nat-cw.backplane.com [208.161.114.67]) by hub.freebsd.org (Postfix) with ESMTP id 1B32C37B405 for ; Fri, 13 Jul 2001 11:47:20 -0700 (PDT) (envelope-from dillon@earth.backplane.com) Received: (from dillon@localhost) by earth.backplane.com (8.11.3/8.11.2) id f6DIlJv67457; Fri, 13 Jul 2001 11:47:19 -0700 (PDT) (envelope-from dillon) Date: Fri, 13 Jul 2001 11:47:19 -0700 (PDT) From: Matt Dillon Message-Id: <200107131847.f6DIlJv67457@earth.backplane.com> To: Leo Bicknell , Drew Eckhardt , hackers@FreeBSD.ORG Subject: Re: Network performance tuning. References: <200107130128.f6D1SFE59148@earth.backplane.com> <200107130217.f6D2HET67695@revolt.poohsticks.org> <20010712223042.A77503@ussenterprise.ufp.org> <200107131708.f6DH8ve65071@earth.backplane.com> <20010713132903.A21847@ussenterprise.ufp.org> Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG : :On Fri, Jul 13, 2001 at 10:08:57AM -0700, Matt Dillon wrote: :> The basic problem with calculating the bandwidth delay product is that :> it is an inherently unstable calculation. It has to be a continuous, : :I think you're doing good work, but I'm concerned you're going down :a road that's going to take a very long time to get right. It is not :necessary to calculate the bandwidth*delay in order to prevent over- :buffering. Preventing overbuffering only requires tracking the maximum :bandwidth*delay value, assuming that we always want the ability to :buffer that much data. I think the number of cases where it decreases :significantly over the peak for a long enough time to make a difference :is minimal. : :Fully knowing the value over time could lead to optimizations like :shrinking the buffers, or attempting to prevent some packet loss by :not over-increasing the window. However oscellation and other issues :I think are going to make this very complex. : :-- :Leo Bicknell - bicknell@ufp.org :Systems Engineer - Internetworking Engineer - CCIE 3440 Well, you'd be surprised. 90% of the world still uses modems, so from the point of view of a web server it would be a big win. The bigger picture is more complex... certainly the instability of the algorithm is a big issue, but it opens the door to research because congestion avoidance and bandwidth and latency guarentees across an arbitrary network ultimately come down to having to deal with something like this. -Matt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message