From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Subject: Re: CLOCK_MONOTONIC datagram timestamps by the kernel Date: Fri, 02 Mar 2007 10:26:57 +0100 Message-ID: <45E7EDE1.30805@free.fr> References: <45E5570E.7050301@free.fr> <200702281555.10309.dada1@cosmosbay.com> <45E5A8AE.3030606@free.fr> <200703011230.50596.dada1@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-net@vger.kernel.org, netdev@vger.kernel.org, Stephen Hemminger , linux.kernel@free.fr To: Eric Dumazet Return-path: Received: from SMT02001.global-sp.net ([193.168.50.54]:49738 "EHLO SMT02001.global-sp.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422982AbXCBJqf (ORCPT ); Fri, 2 Mar 2007 04:46:35 -0500 In-Reply-To: <200703011230.50596.dada1@cosmosbay.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Eric Dumazet wrote: > John wrote: > >> Consider an idle Linux 2.6.20-rt8 system, equipped with a single PCI-E >> gigabit Ethernet NIC, running on a modern CPU (e.g. Core 2 Duo E6700). >> All this system does is time stamp 1000 packets per second. >> >> Are you claiming that this platform *cannot* handle most packets within >> less than 1 microsecond of their arrival? > > Yes I claim it. You expect too much of this platform, unless "most" means > 10 % for you ;) By "most" I meant more than 50%. Has someone tried to measure interrupt latency in Linux? I'd like to plot the distribution of network IRQ to interrupt handler latencies. > If you replace "1 us" by "50 us", then yes, it probably can do it, if "most" > means 99%, (not 99.999 %) I think we need cold, hard numbers at this point :-) > Anyway, if you want to play, you can apply this patch on top of > linux-2.6.21-rc2 (nanosecond resolution infrastructure needs 2.6.21) > I let you do the adjustments for rt kernel. Why does it require 2.6.21? > This patch converts sk_buff timestamp to use new nanosecond infra > (added in 2.6.21) Is this mentioned somewhere in the 2.6.21-rc1 ChangeLog? http://kernel.org/pub/linux/kernel/v2.6/testing/ChangeLog-2.6.21-rc1 Regards.