From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49857) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZbL3G-0001do-P9 for qemu-devel@nongnu.org; Mon, 14 Sep 2015 00:07:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZbL3C-0002Ow-NX for qemu-devel@nongnu.org; Mon, 14 Sep 2015 00:07:34 -0400 Received: from e28smtp01.in.ibm.com ([122.248.162.1]:44329) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZbL3C-0002OJ-1h for qemu-devel@nongnu.org; Mon, 14 Sep 2015 00:07:30 -0400 Received: from /spool/local by e28smtp01.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 14 Sep 2015 09:37:25 +0530 Date: Mon, 14 Sep 2015 09:37:16 +0530 From: Bharata B Rao Message-ID: <20150914040716.GO17433@in.ibm.com> References: <1442194913-26545-1-git-send-email-david@gibson.dropbear.id.au> <1442194913-26545-3-git-send-email-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1442194913-26545-3-git-send-email-david@gibson.dropbear.id.au> Subject: Re: [Qemu-devel] [RFCv2 2/2] spapr: Don't use QOM [*] syntax for DR connectors. Reply-To: bharata@linux.vnet.ibm.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: agraf@suse.de, aik@ozlabs.ru, qemu-devel@nongnu.org, mdroth@linux.vnet.ibm.com, qemu-ppc@nongnu.org, pbonzini@redhat.com On Mon, Sep 14, 2015 at 11:41:53AM +1000, David Gibson wrote: > The dynamic reconfiguration (hotplug) code for the pseries machine type > uses a "DR connector" QOM object for each resource it will be possible > to hotplug. Each of these is added to its owner using > object_property_add_child(owner, "dr-connector[*], ...); > > That works ok, mostly, but it means that the property indices are > arbitrary, depending on the order in which the connectors are constructed. > When we have both memory and cpu hotplug, the connectors will be under the > same parent (at least in the current drafts), meaning the indices don't > correspond to any meaningful ID. > > It gets worse when large amounts of hotpluggable RAM is configured. For > RAM, there's a DR connector object for every 256MB of potential memory. So > if maxmem=2T, for example, there are 8192 objects under the same parent. > > The QOM interfaces aren't really designed for this. In particular > object_property_add() with [*] has O(n^2) time complexity (in the number of > existing children): first it has a linear search through array indices to > find a free slot, each of which is attempted to a recursive call to > object_property_add() with a specific [N]. Those calls are O(n) because > there's a linear search through all properties to check for duplicates. > > By using a meaningful index value, which we already know is unique we can > avoid the [*] special behaviour. That lets us reduce the total time for > creating the DR objects from O(n^3) to O(n^2). > > O(n^2) is still kind of crappy, but it's enough to reduce the startup time > of qemu with maxmem=2T from ~20 minutes to ~4 seconds. > > Signed-off-by: David Gibson > Cc: Bharata B Rao This patch works correctly with both CPU and memory hotplug. Regards, Bharata.