Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754064Ab1B1NKs (ORCPT ); Mon, 28 Feb 2011 08:10:48 -0500 Received: from mail-fx0-f46.google.com ([209.85.161.46]:35376 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754025Ab1B1NKr (ORCPT ); Mon, 28 Feb 2011 08:10:47 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:in-reply-to:references:content-type:date :message-id:mime-version:x-mailer:content-transfer-encoding; b=nvJO5jKnDNzJsekEasFZ/Yqlrg3aZoR/dPXQIEkh54fqF8WVYHEOmpSmRzyj5kQRLX ee3I826RrfaxfhsOZ2pYTimWpXuJbO1pNBVEESLFbIWIc5nIGdOHS5vM3piWnIMDMypT vDFm9rd08Ky0AMjTpIsrrkYsq8fQ9BdSh/6ug= Subject: Re: txqueuelen has wrong units; should be time From: Eric Dumazet To: Jussi Kivilinna Cc: Albert Cahalan , Mikael Abrahamsson , linux-kernel , netdev@vger.kernel.org In-Reply-To: <20110228134338.1241484mkljbz4w0@hayate.sektori.org> References: <1298793252.8726.45.camel@edumazet-laptop> <20110227125540.40754c5y78j9u2m8@hayate.sektori.org> <1298837273.8726.128.camel@edumazet-laptop> <20110228134338.1241484mkljbz4w0@hayate.sektori.org> Content-Type: text/plain; charset="UTF-8" Date: Mon, 28 Feb 2011 14:10:40 +0100 Message-ID: <1298898640.2941.256.camel@edumazet-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2878 Lines: 67 Le lundi 28 février 2011 à 13:43 +0200, Jussi Kivilinna a écrit : > 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) > > > > Accepting a packet at t0, and dropping it later at t0+limit without > > giving any indication to caller is a problem. > > > > 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. > > > > Would it be better to implement this as generic feature instead of > qdisc specific? Have qdisc_enqueue_root do ewma check: Problem is you can have several virtual queues in a qdisc. For example, pfifo_fast has 3 bands. You could have a global ewma with high values, but you still want to let a high priority packet going through... -- 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/