From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Deegan Subject: Re: [PATCH 3 of 3] KEXEC: Allocate crash structures in low memory Date: Fri, 30 Dec 2011 11:19:43 +0000 Message-ID: <20111230111943.GA27359@ocelot.phlegethon.org> References: <4EFC8C73020000780007C160@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <4EFC8C73020000780007C160@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich Cc: andrew.cooper3@citrix.com, xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org At 15:51 +0000 on 29 Dec (1325173875), Jan Beulich wrote: > >This is part of the "min" option which is trying to have the least > >possible impact. The idea is to have this in low memory, use the > >"console_to_ring" boot option to copy dom0 dmesg into conring, and pass > >its physical address and size in a crash note, so that the crash kernel > >environment grab it all. > > Why is the console ring *that* important? I would have thought > that proper register values and stack contents are much more > significant for analysis of a crash. The console ring has been _very_ useful in diagnosing bugs from field reports, especially things like guest-level watchdog timeouts and refcounting errors that cause a crash after the interesting event has passed. If nothing else it lets you verify the user's description of the system, and saves a round-trip of 'please try to set up a serial logger and reproduce the bug'). (I agree, though, that using a 64-bit crash kernel would be a much better idea). Tim.