From mboxrd@z Thu Jan 1 00:00:00 1970 From: Octavian Purdila Subject: Re: [rfc] new sk_buff member: hwstamp Date: Mon, 14 Jul 2008 21:30:12 +0300 Message-ID: <200807142130.12375.opurdila@ixiacom.com> References: <200807141843.00845.opurdila@ixiacom.com> <87abgkz8bc.fsf@basil.nowhere.org> <487B9396.1060701@hartkopp.net> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Cc: Andi Kleen , netdev@vger.kernel.org To: Oliver Hartkopp Return-path: Received: from ixia01.ro.gtsce.net ([212.146.94.66]:4586 "EHLO ixro-ex1.ixiacom.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751692AbYGNScS (ORCPT ); Mon, 14 Jul 2008 14:32:18 -0400 In-Reply-To: <487B9396.1060701@hartkopp.net> Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-ID: > > However i feel, that *one* nanosec resolution timestamp (as it already > exists inside the skbuff) is enough. AFAIK the timestamp is only set in > the netif_rx(), when it is not already set by the driver itself. For > that reason i would suggest to create some semi-intelligent offset > calculation inside the driver that makes the skb->tstamp value > correspond with the hw timestamp and therefore transports the high > resolution timestamp requirement into the userspace. > You mean something like here [1] ? The problem for this approach in our usecase (one way delay measurement) is that the real time clock of the CPUs (of the RX and TX ports) is not synchronized, but the hw timestamp (implemented in the NIC/FPGA) is. [1] http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.23-rc4/2.6.23-rc4-mm1/broken-out/sky2-hardware-receive-timestamp-counter.patch Thanks, tavi