Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754960AbbDTMCA (ORCPT ); Mon, 20 Apr 2015 08:02:00 -0400 Received: from smtp-out6.electric.net ([192.162.217.181]:58493 "EHLO smtp-out6.electric.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754548AbbDTMBx (ORCPT ); Mon, 20 Apr 2015 08:01:53 -0400 From: David Laight To: "'Rob Landley'" , Tejun Heo CC: Andrew Morton , "David S. Miller" , Kernel Mailing List , "netdev@vger.kernel.org" Subject: RE: [PATCHSET] printk, netconsole: implement reliable netconsole Thread-Topic: [PATCHSET] printk, netconsole: implement reliable netconsole Thread-Index: AQHQenH3STvsANA5kkmTBKmIAMNrF51VzH0w Date: Mon, 20 Apr 2015 12:00:38 +0000 Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB223B4@AcuExch.aculab.com> References: <1429225433-11946-1-git-send-email-tj@kernel.org> In-Reply-To: Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.202.99.200] Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 X-Outbound-IP: 213.249.233.130 X-Env-From: David.Laight@ACULAB.COM X-PolicySMART: 3396946, 3397078 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id t3KC27sH008017 Content-Length: 1707 Lines: 37 From: Of Rob Landley > Sent: 19 April 2015 08:25 > On Thu, Apr 16, 2015 at 6:03 PM, Tejun Heo wrote: > > In a lot of configurations, netconsole is a useful way to collect > > system logs; however, all netconsole does is simply emitting UDP > > packets for the raw messages and there's no way for the receiver to > > find out whether the packets were lost and/or reordered in flight. > > Except a modern nonsaturated LAN shouldn't do that. > > If you have two machines plugged into a hub, and that's _all_ that's > plugged in, packets should never get dropped. This was the original > use case of netconsole was that the sender and the receiver were > plugged into the same router. > > However, even on a quite active LAN the days of ethernet doing CDMA > requiring retransmits are long gone, even 100baseT routers have been > cacheing and retransmitting data internally so each connection can go > at the full 11 megabytes/second with the backplane running fast enough > to keep them all active at the same time. (That's why it's so hard to > find a _hub_ anymore, it's all routers ... Most machines are plugged into switches (not routers), many of them will send 'pause' frames which the host mac may act on. In which case packet loss is not expected (unless you have broadcast storms when all bets are off). Additionally, within a local network you shouldn't really get any packet loss since no segments should be 100% loaded. So for testing it is not unreasonable to expect no lost packets in netconsole traffic. David ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m???? ????????I?