From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Cochran Subject: Re: Problems obtaining software TX timestamps Date: Thu, 9 Sep 2010 19:32:28 +0200 Message-ID: <20100909173228.GA2657@riccoc20.at.omicron.at> 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> <1284040958.2589.178.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ingo Kofler , netdev@vger.kernel.org To: Eric Dumazet Return-path: Received: from mail-bw0-f46.google.com ([209.85.214.46]:43339 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751800Ab0IIRcj (ORCPT ); Thu, 9 Sep 2010 13:32:39 -0400 Received: by bwz11 with SMTP id 11so1334314bwz.19 for ; Thu, 09 Sep 2010 10:32:38 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1284040958.2589.178.camel@edumazet-laptop> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, Sep 09, 2010 at 04:02:38PM +0200, Eric Dumazet wrote: > Should drivers call it at start_xmit() time, or at tx completion time ? If I could tell you that, I could also describe the sound of one hand clapping. IMHO, it should be done as immediately after the buffer has been handed off to the hardware. Not all MACs have a completion method, so that would at least make the "rule" consistent. In general, the goals of high volume and timestamp accuracy are in conflict (unless you have HW timestamping). If users are relying on SW timestamping, then they should be aware of the fact that high network traffic will spoil their fun. Having said that, I don't know enough about all the different kinds of MACs out there to really answer the question definitively. Richard