From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: hardware time stamps + existing time stamp usage Date: Tue, 21 Oct 2008 09:04:21 +0200 Message-ID: <48FD7EF5.6050805@linux.intel.com> References: <1224253423.17450.211.camel@ecld0pohly> <200810182237.02373.opurdila@ixiacom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Patrick Ohly , netdev@vger.kernel.org, Stephen Hemminger , Ingo Oeser , "Ronciak, John" To: Octavian Purdila Return-path: Received: from mga07.intel.com ([143.182.124.22]:55766 "EHLO azsmga101.ch.intel.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751015AbYJUHEL (ORCPT ); Tue, 21 Oct 2008 03:04:11 -0400 In-Reply-To: <200810182237.02373.opurdila@ixiacom.com> Sender: netdev-owner@vger.kernel.org List-ID: > We can even compute the delta periodically now, to maintain better system - > hardware timestamps synchronization, as we can keep and multiple deltas (each > one associated with a modulo number). The problem with this scheme is that it's unlikely to be precise enough to guarantee monoticity (that is that your delta clock compared to the system clock never goes backwards). And that tends to be a common requirements in system time stamps. Not having that would risk breaking existing applications. My recommendation would be to find some way to use a separate field and also use a separate API. That would also allow you to extend it (e.g. pass down the interface number), so that different time stamps from different interfaces are supported. -Andi