From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: route metrics in jiffies?? Date: Wed, 21 May 2008 13:31:54 -0700 (PDT) Message-ID: <20080521.133154.173559889.davem@davemloft.net> References: <20080521163815.GA5028@sc.homeunix.net> <20080521101053.27db3495@extreme> <20080521114354.31c6807c@extreme> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Stephane_Chazelas@yahoo.fr, netdev@vger.kernel.org To: shemminger@vyatta.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:35590 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S937193AbYEUUb6 (ORCPT ); Wed, 21 May 2008 16:31:58 -0400 In-Reply-To: <20080521114354.31c6807c@extreme> Sender: netdev-owner@vger.kernel.org List-ID: From: Stephen Hemminger Date: Wed, 21 May 2008 11:43:54 -0700 > There is an even bigger mess up. The API for route metrics has several > values encoded in jiffies. This is a problem because there is no good > way to find the internal kernel value of HZ. So all kernel/user ABI's > are supposed to use an absolute value (like milliseconds) or clock_t > which user USER_HZ. > > The problem is that these values are now hardcoded into people's systems > so anyone using the 'ip route' options: rttvar, rtomin, or rtt are broken. > They might be lucky now (but I doubt it). > > I propose doing the right thing and fixing kernel and iproute to always > use milliseconds for these values. To maintain compatibility, the new metric > values will be renumbered. So old kernels don't misinterpret the new values. That is one way to solve the problem. But we could be adding surprises on a source level for people with this approach. Just use new names and leave the old ones alone, with a _MS or similar postfix to them. This is how we've handled this kind of situation in the past.