Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751924Ab1B0Vco (ORCPT ); Sun, 27 Feb 2011 16:32:44 -0500 Received: from sinikuusama.dnainternet.net ([83.102.40.134]:50019 "EHLO sinikuusama.dnainternet.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751819Ab1B0Vcm (ORCPT ); Sun, 27 Feb 2011 16:32:42 -0500 X-Spam-Flag: NO X-Spam-Score: -1.44 Message-ID: <20110227233228.133610ohbha7chk0@hayate.sektori.org> Date: Sun, 27 Feb 2011 23:32:28 +0200 From: Jussi Kivilinna To: Eric Dumazet Cc: Albert Cahalan , Mikael Abrahamsson , linux-kernel , netdev@vger.kernel.org Subject: Re: txqueuelen has wrong units; should be time References: <1298793252.8726.45.camel@edumazet-laptop> <20110227125540.40754c5y78j9u2m8@hayate.sektori.org> <1298837273.8726.128.camel@edumazet-laptop> In-Reply-To: <1298837273.8726.128.camel@edumazet-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; DelSp="Yes"; format="flowed" Content-Disposition: inline Content-Transfer-Encoding: 8bit User-Agent: Internet Messaging Program (IMP) H3 (4.3.7) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2454 Lines: 64 Quoting Eric Dumazet : > Le dimanche 27 février 2011 à 12:55 +0200, Jussi Kivilinna a écrit : >> Quoting Albert Cahalan : >> >> > On Sun, Feb 27, 2011 at 2:54 AM, Eric Dumazet >> wrote: >> >> Le dimanche 27 février 2011 à 08:02 +0100, Mikael Abrahamsson a écrit : >> >>> On Sun, 27 Feb 2011, Albert Cahalan wrote: >> >>> >> >>> > Nanoseconds seems fine; it's unlikely you'd ever want >> >>> > more than 4.2 seconds (32-bit unsigned) of queue. >> > ... >> >> Problem is some machines have slow High Resolution timing services. >> >> >> >> _If_ we have a time limit, it will probably use the low resolution (aka >> >> jiffies), unless high resolution services are cheap. >> > >> > As long as that is totally internal to the kernel and never >> > getting exposed by some API for setting the amount, sure. >> > >> >> I was thinking not having an absolute hard limit, but an EWMA based one. >> > >> > The whole point is to prevent stale packets, especially to prevent >> > them from messing with TCP, so I really don't think so. I suppose >> > you do get this to some extent via early drop. >> >> I made simple hack on sch_fifo with per packet time limits >> (attachment) this weekend and have been doing limited testing on >> wireless link. I think hardlimit is fine, it's simple and does >> somewhat same as what packet(-hard)limited buffer does, drops packets >> when buffer is 'full'. My hack checks for timed out packets on >> enqueue, might be wrong approach (on other hand might allow some more >> burstiness). >> > > > Qdisc should return to caller a good indication packet is queued or > dropped at enqueue() time... not later (aka : never) Ok, it is ugly hack ;) I got idea of dropping head from pfifo_head_drop. > > Accepting a packet at t0, and dropping it later at t0+limit without > giving any indication to caller is a problem. Ok. > > This is why I suggested using an EWMA plus a probabilist drop or > congestion indication (NET_XMIT_CN) to caller at enqueue() time. > > The absolute time limit you are trying to implement should be checked at > dequeue time, to cope with enqueue bursts or pauses on wire. > Ok. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/