From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53280) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f5kgz-0006bA-8Z for qemu-devel@nongnu.org; Tue, 10 Apr 2018 00:15:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f5kgw-0003qZ-Gf for qemu-devel@nongnu.org; Tue, 10 Apr 2018 00:15:37 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:36956) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f5kgw-0003pY-8B for qemu-devel@nongnu.org; Tue, 10 Apr 2018 00:15:34 -0400 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w3A4Anne077385 for ; Tue, 10 Apr 2018 00:15:33 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0a-001b2d01.pphosted.com with ESMTP id 2h8jp2pqsc-1 (version=TLSv1.2 cipher=AES256-SHA256 bits=256 verify=NOT) for ; Tue, 10 Apr 2018 00:15:32 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 10 Apr 2018 05:15:29 +0100 Date: Tue, 10 Apr 2018 09:45:21 +0530 From: Bharata B Rao Reply-To: bharata@linux.vnet.ibm.com References: <20180409062538.1095-1-bharata@linux.vnet.ibm.com> <20180410030245.GF3361@umbus.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180410030245.GF3361@umbus.fritz.box> Message-Id: <20180410041521.GA14855@in.ibm.com> Subject: Re: [Qemu-devel] [RFC PATCH v2] spapr: Support ibm, dynamic-memory-v2 property List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: qemu-devel@nongnu.org, qemu-ppc@nongnu.org, nfont@linux.vnet.ibm.com, mwb@linux.vnet.ibm.com, imammedo@redhat.com On Tue, Apr 10, 2018 at 01:02:45PM +1000, David Gibson wrote: > On Mon, Apr 09, 2018 at 11:55:38AM +0530, Bharata B Rao wrote: > > The new property ibm,dynamic-memory-v2 allows memory to be represented > > in a more compact manner in device tree. > > I still need to look at this in more detail, but to start with: > what's the rationale for this new format? > > It's more compact, but why do we care? The embedded people always > whinge about the size of the deivce tree, but I didn't think that was > really a concern with PAPR. Here's a real example of how this has affected us earlier: SLOF's CAS FDT buffer size was initially 32K, was changed to 64k to support 1TB guest memory and again changed to 2MB to support 16TB guest memory. With ibm,dynamic-memory-v2 we are less likely to hit such scenarios. Also, theoretically it should be more efficient in the guest kernel to handle LMB-sets than individual LMBs. We aren't there yet, but I believe grouping of LMBs should eventually help us do memory hotplug at set (or DIMM) granularity than at individual LMB granularity (Again theoretical possibility) Regards, Bharata.