From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55247) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZbLbT-0001Ro-3s for qemu-devel@nongnu.org; Mon, 14 Sep 2015 00:42:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZbLbP-0006XH-Tm for qemu-devel@nongnu.org; Mon, 14 Sep 2015 00:42:55 -0400 Received: from e23smtp08.au.ibm.com ([202.81.31.141]:57031) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZbLbP-0006Wi-Aa for qemu-devel@nongnu.org; Mon, 14 Sep 2015 00:42:51 -0400 Received: from /spool/local by e23smtp08.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 14 Sep 2015 14:42:48 +1000 Date: Mon, 14 Sep 2015 10:11:50 +0530 From: Bharata B Rao Message-ID: <20150914044150.GP17433@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> <20150914040716.GO17433@in.ibm.com> <20150914041459.GJ2547@voom.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150914041459.GJ2547@voom.fritz.box> 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 02:14:59PM +1000, David Gibson wrote: > On Mon, Sep 14, 2015 at 09:37:16AM +0530, Bharata B Rao wrote: > > 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. > > Care to send a Reviewed-by and/or Tested-by in that case? Sorry, Tested-by: Bharata B Rao