From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: Problems obtaining software TX timestamps Date: Thu, 09 Sep 2010 16:02:38 +0200 Message-ID: <1284040958.2589.178.camel@edumazet-laptop> References: <4C877D8A.6040002@edu.uni-klu.ac.at> <1283958771.2748.85.camel@edumazet-laptop> <4C87FE60.7090209@edu.uni-klu.ac.at> <20100909063541.GA3305@riccoc20.at.omicron.at> <4C889A1E.6050405@edu.uni-klu.ac.at> <20100909135716.GA8706@riccoc20.at.omicron.at> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Ingo Kofler , netdev@vger.kernel.org To: Richard Cochran Return-path: Received: from mail-fx0-f46.google.com ([209.85.161.46]:39873 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751857Ab0IIOCo (ORCPT ); Thu, 9 Sep 2010 10:02:44 -0400 Received: by fxm16 with SMTP id 16so872484fxm.19 for ; Thu, 09 Sep 2010 07:02:43 -0700 (PDT) In-Reply-To: <20100909135716.GA8706@riccoc20.at.omicron.at> Sender: netdev-owner@vger.kernel.org List-ID: Le jeudi 09 septembre 2010 =C3=A0 15:57 +0200, Richard Cochran a =C3=A9= crit : > On Thu, Sep 09, 2010 at 10:26:06AM +0200, Ingo Kofler wrote: > > Thank you very much for this clarification. Are there any drawbacks > > with this approach, e.g. performance issues? Honestly, I am just > > wondering why driver developers do not add this single line if it's > > that easy.... >=20 > Adding the line only tests one flag, so it is not a huge performance > hit. This fix is very recent, that is why it has not been used in MAC > drivers yet. Should drivers call it at start_xmit() time, or at tx completion time ? 1) start_xmit() time : Earlier than real hardware xmit (with up to 1000 packets queued in TX ring, delay might be very large) 2) tx completion time : After real hardware xmit (on tg3, ethtool -c gives : tx-usecs: 72 , tx-frames: 53, so we can have a delay of 72 us before NIC acknowledges the frame xmit)