From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Kiper Subject: Re: [PATCH for-xen-4.5] console: increase initial conring size Date: Wed, 3 Dec 2014 16:37:17 +0100 Message-ID: <20141203153717.GM16236@olila.local.net-space.pl> References: <1417532274-28976-1-git-send-email-daniel.kiper@oracle.com> <547DE1BD02000078000C2DEF@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1XwBzg-0000IK-Ch for xen-devel@lists.xenproject.org; Wed, 03 Dec 2014 15:37:32 +0000 Content-Disposition: inline In-Reply-To: <547DE1BD02000078000C2DEF@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich Cc: keir@xen.org, ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, andrew.cooper3@citrix.com, xen-devel@lists.xenproject.org List-Id: xen-devel@lists.xenproject.org On Tue, Dec 02, 2014 at 03:58:53PM +0000, Jan Beulich wrote: > >>> Daniel Kiper 12/02/14 3:58 PM >>> > >In general initial conring size is sufficient. However, if log > >level is increased on platforms which have e.g. huge number > >of memory regions (I have an IBM System x3550 M2 with 8 GiB RAM > >which has more than 200 entries in EFI memory map) then some > >of earlier messages in console ring are overwritten. It means > >that in case of issues deeper analysis can be hindered. Sadly > >conring_size argument does not help because new console buffer > >is allocated late on heap. It means that it is not possible to > >allocate larger ring earlier. So, in this situation initial > >conring size should be increased. My experiments showed that > >even on not so big machines more than 26 KiB of free space are > >needed for initial messages. In theory we could increase conring > >size buffer to 32 KiB. However, I think that this value could be > >too small for huge machines with large number of ACPI tables and > >EFI memory regions. Hence, this patch increases initial conring > >size to 64 KiB. > > > >Signed-off-by: Daniel Kiper > > I think it was made clear before that just saying "for-xen-4.5" without any > further rationale is insufficient. Please explain what makes this so important > a change that it needs to go in now. What is not clear in commit message? It describes a bug, how to fix it and why in that way. Do you need anything else? > Apart from that, as Olaf validly replied, setting up a dynamically allocated > buffer earlier would seem like a much better course of action. I though about that before posting this patch (I did not know beforehand about Olaf's work made in 2011). However, I stated that it is too late to make so intrusive changes. I think we should (sadly) apply this "band-aid" right now because, as you can see, this bug hits more and more people. On the other hand I agree that we should finally fix this issue in better way. Even I am able to add this thing to my TODO list but it is quite long so I do not know when it will happen. Daniel