Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753018Ab1B1Vp7 (ORCPT ); Mon, 28 Feb 2011 16:45:59 -0500 Received: from mail-gy0-f174.google.com ([209.85.160.174]:45167 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752477Ab1B1Vp5 convert rfc822-to-8bit (ORCPT ); Mon, 28 Feb 2011 16:45:57 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=OvLZuiikWhLHBFEOn65zl+6C++J8yHkFp5y0HSzRmV8+Q32t6XJJXaoB4FsL3qkbVf +SFrBCDsUF9JSrDT1F6Ttwy1w39FTeVeZZ9FAohRvGM8Ttt7PTyBLN831BgS/08lU7Qx Va0oPtmSDosP4diZIUAjsQjVS2nYUhCds9t8k= MIME-Version: 1.0 In-Reply-To: <20110228165501.GC2515@tuxdriver.com> References: <1298793252.8726.45.camel@edumazet-laptop> <20110227125540.40754c5y78j9u2m8@hayate.sektori.org> <1298837273.8726.128.camel@edumazet-laptop> <20110228161115.GB2515@tuxdriver.com> <1298911694.2941.639.camel@edumazet-laptop> <20110228165501.GC2515@tuxdriver.com> Date: Mon, 28 Feb 2011 16:45:56 -0500 Message-ID: Subject: Re: txqueuelen has wrong units; should be time From: John Heffner To: "John W. Linville" Cc: Eric Dumazet , Jussi Kivilinna , Albert Cahalan , Mikael Abrahamsson , linux-kernel , netdev@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1851 Lines: 42 On Mon, Feb 28, 2011 at 11:55 AM, John W. Linville wrote: > On Mon, Feb 28, 2011 at 05:48:14PM +0100, Eric Dumazet wrote: >> Le lundi 28 f?vrier 2011 ? 11:11 -0500, John W. Linville a ?crit : >> > On Sun, Feb 27, 2011 at 09:07:53PM +0100, Eric Dumazet wrote: >> > >> > > 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. >> > >> > Can you elaborate on what problem this causes? ?Is it any worse than >> > if the packet is dropped at some later hop? >> > >> > Is there any API that could report the drop to the sender (at >> > least a local one) without having to wait for the ack timeout? >> > Should there be? >> > >> >> Not all protocols have ACKS ;) >> >> dev_queue_xmit() returns an error code, some callers use it. > > Well, OK -- I agree it is best if you can return the status at > enqueue time. ?The question becomes whether or not a dropped frame > is worse than living with high latency. ?The answer, of course, still > seems to be a bit subjective. ?But, if the admin has determined that > a link should be low latency...? Notably, TCP is one caller that uses the error code. The error code is functionally equivalent to ECN, one of whose great advantages is reducing delay jitter. If TCP didn't get the error, that would effectively double the latency for a full window of data, since the dropped segment would not be retransmitted for an RTT. -John -- 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/