From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58051) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZbOtJ-0007BQ-Gk for qemu-devel@nongnu.org; Mon, 14 Sep 2015 04:13:34 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZbOtF-0008Nw-3k for qemu-devel@nongnu.org; Mon, 14 Sep 2015 04:13:33 -0400 Received: from mail-pa0-f49.google.com ([209.85.220.49]:34955) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZbOtE-0008Nk-Ua for qemu-devel@nongnu.org; Mon, 14 Sep 2015 04:13:29 -0400 Received: by pacfv12 with SMTP id fv12so140140428pac.2 for ; Mon, 14 Sep 2015 01:13:26 -0700 (PDT) References: <1442194913-26545-1-git-send-email-david@gibson.dropbear.id.au> <1442194913-26545-3-git-send-email-david@gibson.dropbear.id.au> From: Alexey Kardashevskiy Message-ID: <55F6819E.7080902@ozlabs.ru> Date: Mon, 14 Sep 2015 18:13:18 +1000 MIME-Version: 1.0 In-Reply-To: <1442194913-26545-3-git-send-email-david@gibson.dropbear.id.au> Content-Type: text/plain; charset=koi8-r; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFCv2 2/2] spapr: Don't use QOM [*] syntax for DR connectors. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson , mdroth@linux.vnet.ibm.com, bharata@linux.vnet.ibm.com Cc: pbonzini@redhat.com, qemu-ppc@nongnu.org, agraf@suse.de, qemu-devel@nongnu.org On 09/14/2015 11:41 AM, 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. 20 minutes sounds really cool :) > > Signed-off-by: David Gibson > Cc: Bharata B Rao Reviewed-by: Alexey Kardashevskiy > --- > hw/ppc/spapr_drc.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c > index 68e0c3e..2f95259 100644 > --- a/hw/ppc/spapr_drc.c > +++ b/hw/ppc/spapr_drc.c > @@ -451,13 +451,16 @@ sPAPRDRConnector *spapr_dr_connector_new(Object *owner, > { > sPAPRDRConnector *drc = > SPAPR_DR_CONNECTOR(object_new(TYPE_SPAPR_DR_CONNECTOR)); > + char *prop_name; > > g_assert(type); > > drc->type = type; > drc->id = id; > - object_property_add_child(owner, "dr-connector[*]", OBJECT(drc), NULL); > + prop_name = g_strdup_printf("dr-connector[%"PRIu32"]", get_index(drc)); > + object_property_add_child(owner, prop_name, OBJECT(drc), NULL); > object_property_set_bool(OBJECT(drc), true, "realized", NULL); > + g_free(prop_name); > > /* human-readable name for a DRC to encode into the DT > * description. this is mainly only used within a guest in place > -- Alexey