From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [Xen-devel] Re: [PATCH] Two patches fixing regression introduced by 'x86-64, mm: Put early page table high' Date: Mon, 2 May 2011 14:08:02 -0400 Message-ID: <20110502180802.GA7498@dumpdata.com> References: <1304356942-17656-1-git-send-email-konrad.wilk@oracle.com> <4DBEEA69.7010000@zytor.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4DBEEA69.7010000@zytor.com> Sender: linux-kernel-owner@vger.kernel.org To: "H. Peter Anvin" Cc: xen-devel@lists.xensource.com, yinghai@kernel.org, linux-kernel@vger.kernel.org, stefano.stabellini@eu.citrix.com List-Id: xen-devel@lists.xenproject.org On Mon, May 02, 2011 at 10:31:21AM -0700, H. Peter Anvin wrote: > On 05/02/2011 10:22 AM, Konrad Rzeszutek Wilk wrote: > > > > But we haven't come up with an acceptable general solution yet, so this > > patchset provides a workaround for the problem. Peter, Yinghai - what would be > > the best forum/email/conference to hammer out a general solution for this? > > > > Currently, there are couple of ways of fixing this: > > - use pvops hooks: http://marc.info/?i=1302607192-21355-2-git-send-email-stefano.stabellini@eu.citrix.com > > - have a workaround in Xen MMU's early bootup code (which is what these > > two patches to this email have). > > - or remove the patch introducing the regression altogether. > > > > Foremost important is to fix the regression, and attached patches > > achieve that. I want to remove this workaround patch when we > > hammer out more appropriate semantics for the page table creation - but > > that will take some time and the runway to do that in 2.6.39 is gone. > > > > My inclination would be to apply your workaround -- are there any > adverse effects to doing that? There is a bootup slowdown (not noticeable). That is because we call the 'memblock_find_range' function on every PTE table creation (only during bootup of course). Testing wise, on the machines on which the regression occurred, with these two patches the regression disappears - so that is a good sign. I am testing it on some more today to assure myself I am not missing anything. > > -hpa > > [Sorry if I have missed any emails recently... apparently my email was > significantly on the fritz over the last few days.] Yikes - I hate when that happens. I was wondering why you went so silent on some of the emails.